On the fringes of the Botanic Gardens sits a secret World War II air-raid shelter that had gone undetected for decades.
The approximately 4m-tall, 5m-wide, 10m-long sand-coloured shelter was shrouded in thick vegetation and a towering ficus tree had taken root above it.
The structure was discovered only in 2012 by a staff member who had been wandering through the area. Describing it as "rather impressive", the Gardens' director, Dr Nigel Taylor, told The Straits Times that about 2.5m of earth had to be removed before its door was found.
The historical site is also home to what is possibly a family burial ground with three sets of old Chinese tombs - one of which is the oldest known Chinese grave still in its original location.
The National Parks Board said it is exploring the idea of organising guided tours of the site, which is now cordoned off from the public. Details such as the site's location will be released at a later date.
Last year, NParks commissioned a team of archaeologists from the Iseas-Yusof Ishak Institute to study the area.
To access the bunker, the team had to break through its entrance, which had been sealed with bricks and a layer of cement plastering.
Nothing was found within but researchers said that the shelter's layout - two antechambers at its entrance leading to a larger main chamber - was likely designed to diffuse a direct blast from the entrance or act as smoke or fire stops.
Researchers added that the lack of ventilation shafts meant that the shelter had probably been designed to protect important property or records and was not intended to house people.
Its date of construction is unclear, but it appears in a 1948 aerial photograph. Iseas archaeologist Lim Chen Sian, who led the study, said the structure could have been built around the 1930s in the lead-up to the war. "Back then, a lot of people built their own private bomb shelters in their gardens," he said.
It is unclear who used the shelter as the area has changed hands multiple times throughout its history - from the old Botanic Gardens, to Raffles College, the Singapore University, the National Institute of Education and the former Singapore Management University.
While the Iseas report said that the structure could have been used by Raffles College, Dr Taylor's conjecture is that it may have been used by Japanese forces, which had occupied the college as their headquarters.
The archaeological survey also involved the study of the tombs adjacent to the bunker. The team carefully excavated parts of the site, conducted topographic documentation and studied the tombs' iconography and inscriptions.
Iseas anthropologist and cemetery specialist Hui Yew-Foong said two sets of graves, dated 1842 and 1881, are significant and provide "fertile material for studying the evolution of Chinese tombs in Singapore and the region".
He said the 1842 grave gives an idea of the materials, workmanship and design used for the grave of a moderately wealthy Chinese family in early colonial Singapore.
The Iseas team said Qiu Zheng Zhi, who lies in the 1842 tomb, could have come to Singapore from Penang instead of from his ancestral home in Fujian, China.
Meanwhile, Qiu's wife, Li Ci Shu, had been given an honorific posthumous name to commemorate her virtues - a practice commonly seen in Bukit Brown, where such names are found conferred on female ancestors.
The researchers added that the 1881 grave is an early example of an inter-ethnic union. The husband, Huang Hui Shi, from Fujian, China, married a woman called Si Ma Ni, a non-Chinese name.
They believe this could have been a "transliteration" of the Indonesian-sounding "Nisma" and that she could have come from the Dutch East Indies.
The third grave lacked inscription on its headstone. But the study said it could have been built in the mid-to-late-19th century, or the first quarter of the 20th century.
Heritage enthusiasts had highlighted the presence of the tombs to the authorities in 2006, which led to NParks shelving its plans for a new extension for landscaped horticulture displays.
Dr Taylor, who drew up the proposed boundary of the World Heritage Site to include the graves, said he did so to protect them. He said: "There's a possibility that the family has some historical connections with the Gardens or, given the date of the first burial, even go back beyond the Gardens' history."
The burial and bunker site had once been British military reserve land. It had been used by some Chinese who cultivated indigo and farmed fruit trees.
In 1879, the area became part of the Botanic Gardens' Economic Garden for the growth and experimentation of potential economic crops, including rubber.
A version of this article appeared in the print edition of The Sunday Times on December 13, 2015, with the headline More history unearthed at Botanic Gardens. Subscribe