An ongoing note in Ms Sancia Ng's mobile phone serves as a record of where she has been.

The 30-year-old has gone on many solo trips in the past few years, including about 10 to Japan, several to Europe, and jaunts to other countries including the United States, South Korea, Cambodia, Australia and Turkey.

The sales trader in a bank started travelling alone in 2011.

It began on a whim, but these trips have since become annual must-dos and she embarks on at least two of them each year.

"Solo travel is liberating. The solo traveller is alone, but never lonely. Unhindered by itineraries, I love being able to observe people in my own space and at my own pace," she says.

She is among a growing number of female solo travellers here and in Asia.

Like Ms Ng, they are drawn to exploring the world on their own because such trips offer them new experiences, allow them to immerse in local culture and give them opportunities for personal growth.

Locally, data from global homesharing platform Airbnb reveals that the number of outbound Singaporean female solo travellers has doubled from Jan 31 last year to Jan 31 this year.

In contrast, the number of male solo travellers has remained consistent over the years.

Ms Robin Kwok, Airbnb's country manager of South-east Asia, Hong Kong and Taiwan, says the trend is seen elsewhere in Asia. Its data shows that women from Japan, China, Taiwan and South Korea are among the world's most frequent solo travellers.

Travel planning and booking site TripAdvisor's Women and the World Travel Survey in 2015 - a study it launched in 2014 to gain insight into the market - found that almost half of its South-east Asian respondents said they had travelled alone - "a significant rise" from the 36 per cent from the year before.

The survey's 2014 edition had also found that 75 per cent of the 636 South-east Asian women polled enjoy solo travelling as the experience changes them and makes them feel more confident.

Hotels and tour operators have caught on and are rolling out carrots to reel in the female solo traveller.

At India's The Leela Palace New Delhi, a five-star hotel, solo female travellers are offered a pampering and safe stay under the hotel's Kamal package - specifically tailored for women.

These travellers are attended to by female butlers and housekeepers, and have access to a personal female chef. They are driven from the airport to the hotel by a female chauffeur and stay on the hotel's exclusive ladies-only floor, which comes with a security guard, also female.

The hotel's spokesman says demand for the package, launched in 2011, has "increased 10-fold" in the past two years and "is growing with each passing month".

Various properties on third-party hotel booking website Small Luxury Hotels Of The World have also been actively catering to the needs of solo female travellers.

At Dukes London, such guests are assigned a female employee to escort them and handle all room and housekeeping requirements; and La Suite Kobe Harborland in Japan offers female-oriented amenities, including a facial mask, moisturising gloves and a ladies-only spa.

Premium tour operator Insight Vacations is also in the process of planning a female-targeted trip itinerary.

Beyond these special arrangements, solo female travellers say the draw of travelling alone lies in the people they meet and the adventures that await them.

Real estate agent Ang Geok Bee, 41, hit it off with an Italian man in a travel cafe while she was holidaying in Barcelona, Spain, more than 20 years ago.

They are still in touch and she has visited him several times in Italy.

"We chat about everything - our lives, careers, family. I find the friendship meaningful," she says.

Bank employee Amy Soh, 31, went on a solo trip for the first time in January last year.

"I had just turned 30 and wanted to step out of my comfort zone after hitting the milestone for some me-time," she says.

She booked herself a yoga retreat in Koh Samui, Thailand, to "connect with myself" and says she emerged from the trip feeling physically and mentally refreshed.

"I hope to make this an annual thing," she says.

Chance to challenge herself physically

Although she considers herself unathletic, Ms Aprilyn Chan succeeded in doing a solo hike across a chain of mountains.

It took her 10 hours in the same day to trek the rugged coastline that links the mediaeval fishing villages of Italy's Cinque Terre - a hike that guidebooks usually advise travellers to take a few days to do.

"A villager looked at my petite frame and told me to stop hiking when I was on the last leg of my journey. I contemplated doing so because I was dead beat by then. But I decided not to give up," says the manager in a recruitment consultancy of the 2015 journey.

Such experiences are quintessential to her solo trips each year.

"I look to challenge myself mentally and physically, broaden my understanding of the world and discover myself anew," she says.

She began ticking off a bucket list of "firsts" in 2014 when she made her first solo trip to Spain - her first time venturing out of Asia.

Last year, the 30-year-old singleton kayaked for the first time in Greece.

This year, in Africa, she went shark cage-diving, skydiving and abseiled from a 1,000m-high mountain, snorkelled with seals, and went on a two-week wildlife volunteering programme.

Her friends had mixed reactions to her solo travels.

Some were encouraging, but others found it "weird" that she would want to take on such "dangerous" experiences.

One friend even suggested that she carry a knife, so that she could stab anyone who "tries to be funny with you".

Ms Chan realised that there were negative perceptions of female solo travel among Singaporeans.

"We seem to think of the worst things that can happen. There is also a stigma - that it's a very lonely activity," she says, adding that she has few friends here who have attempted solo trips or who would consider them.

"The more that people are against the idea of solo travelling, the more I want to do it," she says.

After Spain, there was no looking back.

That trip gave her immense self-satisfaction - she managed to navigate her way around the country despite her poor sense of direction.

The journey to a location took much longer than that indicated on the maps. But that did not matter to Ms Chan - only reaching the destination did.

In adopting that mindset on all her trips to date, she is enjoying the time she has to herself and learning how to solve problems along the way.

"Sometimes, things don't turn out the way I plan. But there's no point in being frustrated because the problem doesn't go away," she says. "It's far more useful to think, look around and ask for help."

Taking the initiative to speak to strangers is also something she has learnt to do on her solo trips.

These strangers, she says, have helped her to decipher road signs, given her directions and helped her get to airports on time.

Some of them have even become friends - such as two male Swedish teenagers she met recently in Africa. The trio got on so well that she will be flying to Bangkok to meet them again later this year for a holiday.

She says: "It's amazing that I could find such compatible travel partners when it's sometimes hard to travel even with friends."

No longer awkward doing things alone

Not even a broken foot could keep public relations specialist Olivia Lee, 24, from doing a solo trip.

While nursing a broken fourth metatarsal on her right foot in December, she holidayed for eight days in Krabi, a resort town in Thailand.

"I went clubbing, swimming, walked around a lot and even explored caves filled with rocks," she says.

Her right foot was always sore and swollen by the end of the day. But to the plucky young woman, it was a case of "no pain, no gain".

She embarked on her first solo trip in 2015 and has done five such trips in under two years.

She had always been intrigued by the idea of solo travelling.

"I wanted to know what it'd be like spending time with myself, immersed in my own thoughts," she says.

An opportunity surfaced when she had a break after graduating from university in 2015 and she decided to book a 12-day trip to Taiwan.

There, she experienced what it was like having almost all her meals by herself and watched a movie in a cinema alone for the first time in her life.

After that trip, she was hooked.

"Unlike trips with friends, where you have to accommodate others, I could concentrate on my own wants and do whatever I wanted," she says.

As these solo trips increased in frequency - Boracay last October, Krabi and Bintan in December and Cebu last month, her parents became increasingly worried.

"They say I'm a daredevil. They can't understand why I must do these trips," she says of her 51-year-old security guard father's and 50-year-old factory worker mother's concerns. Ms Lee has a younger brother, 20, a polytechnic student.

The idea of solo-tripping was also met with scepticism from both male and female friends.

Some admitted that they would find travelling alone a lonesome affair.

"Others asked: 'Is it safe for you? You're female, you know.' I would retort, saying, 'So?'" she says.

The bachelorette adds that while there were many periods when she was alone, she never felt lonely.

"There's always something new to see or do," she says.

She has yet to feel unsafe on her trips, but did feel harassed once - in Boracay.

She was at a bar listening to a live band with some hostel mates, when a local approached her and persisted in yanking her towards him.

He was "aggressive" and she recalls feeling uncomfortable.

She asked her hostel mates for help. They surrounded her protectively and the man left her alone after that.

She says she has become more "bold and spontaneous" where trip planning is concerned.

She planned her inaugural solo trip to Taiwan to a T, but for her most recent five-day trip to Cebu, she booked only a day's worth of accommodation and booked the subsequent nights while there.

This way, she does not feel tied down to one place, she says.

Thanks to her solo travels, dining alone here is no longer a source of awkwardness for her. Watching movies alone here is also a newfound habit.

She catches people glancing and staring at her when she is doing these activities or travelling alone.

"I can imagine what is going through their minds. They are probably thinking, 'Why?'

"I'd say to them, 'Why not?'"

Correction note: An earlier version of the article referred erroneously to Ms Robin Kwok as Mr Robin Kwok. We are sorry for the error.