If you have 6 or more hours in hand before you catch your connecting flight from Changi Airport, my top recommendation would be to take their free Singapore tour. In fact, many years ago this is how I spent my 18 hours layover at Changi Airport by taking their two free tours, freshening up in a transit hotel and just walking around the airport. The tours are offered from terminals T2 and T3 and you can register for the tour from the transit area itself. You may need to check the Visa requirements applicable to you at the counter. There are two tours offered—Heritage Tour and City Sights Tour. Heritage Tour happens 6 times a day between 8:30 AM and 2:30 PM while City Sights Tour happens 3 times between 3 PM and 6:30 PM. Heritage Tour covers the cultural sites of Singapore, such as Little India, China Town and Kampong Glam while City Sights Tour covers the laser show at Marina Bay Sands and Garden Rhapsody at Gardens by the Bay. Both the tours take you to the famous Merlion, the symbol of Singapore, for a photo opportunity. Each tour lasts for roughly two and a half hours. As per the current regulations, you can take a tour every time you transit through Singapore.