1. What is the Singapore-Malaysia Leaders' Retreat?
This is an annual meeting between Prime Minister Lee Hsien Loong and his Malaysian counterpart Prime Minister Najib Razak. The highlight is a "4-eye" session in which the two leaders hold frank discussions alone without their officials or delegations.
These retreats have yielded major bilateral breakthroughs, such as in 2010, when the two leaders came to an agreement about Malayan Railway land in Singapore, an issue that had been unresolved for two decades. In 2013, they also conceived of a high-speed rail link that would cut travel time between Singapore and Kuala Lumpur to 90 minutes.
Since 2012, the retreats have taken place annually, alternating in location between Singapore and Malaysia.
2. Why a high-speed rail link?
The link has been billed as a "game-changer" for both countries by the two leaders as it will create opportunities for businesses and people, and draw people from Singapore and Malaysia closer together. With the high-speed rail, people who live in Kuala Lumpur can work in Singapore, and vice versa.
This means that "you can go up to KL in a day, have lunch and return to Singapore, or you come down to Spore for a day, do business because now hawker food not quite so good...," PM Lee said on Tuesday to laughter at his press conference with Mr Najib.
The Malaysian leader said the high-speed rail was an "iconic project" and described it as a development that would "really be very very significant" for the two neighbours.
3. When will this high-speed rail link be completed?
The original target date for completion was 2020. But the two leaders said on Tuesday that this was unrealistic due to the complexities involved in the 350km-long rail project. The two sides have yet to iron out major issues like where the funding will come from and how the line will be structured and built.
But they have committed to coming to an agreement on all major issues by the end of this year. Then, a new target date for completion will be announced.
Mr Najib estimated that the design process would take one year, the tender process another year, and the building of the link five years.
4. Where will the Singapore terminus for the high-speed rail link be sited?
The terminus will be in Jurong East, although its exact location has not been divulged. PM Lee said on Tuesday that the Jurong East location dovetailed with the Government's plans to make the Jurong Lake area the second central business district. Analysts said the announcement will boost property value and interest in the Jurong Gateway area, with some predicting that multi-national companies could move their offices there.
5. What else did the two leader discuss at their 2015 retreat?
Connectivity of other forms between Singapore and Malaysia was also on the agenda at the 2015 retreat, with PM Lee and PM Najib and their delegations discussing how to reduce congestion on the Causeway, and also touched on the Rapid Transit System in Johor Bahru that would be linked to Singapore's MRT network. In Singapore, the linking station will be Woodlands North on the Thomson-East Coast line, but the Malaysian side has yet to announce where it will locate its station.
A "Friendship Bridge," proposed at the retreat in 2014 as a symbol of friendship between Singapore and Malaysia, was also discussed on Tuesday. It would be the third bridge crossing between Malaysia and Singapore, after the Causeway and the Second Link at Tuas.
On the sidelines of the retreat, an agreement was signed to boost ferry services from Changi Ferry Terminal to Tanjung Belungkor in Southeastern Johor, which is near the tourist spot of Desaru. The ferry currently runs twice a day on weekdays, and four times a day on weekends and public holidays.
The next retreat will be in Malaysia in 2016. Prime Minister Najib said he has not decided on the location, "but we'll make it exciting".