Yes, you must go through immigration and customs to visit the Jewel Changi Airport complex, as it is located in the "landside" or public area of the airport. Jewel is not part of the secure transit area where the boarding gates are located. If you are a transit passenger with a layover, you will need to clear Singapore Arrival Immigration, which requires a valid passport, an SG Arrival Card (submitted online), and potentially a visa depending on your nationality. Once you clear immigration, you can walk directly from Terminals 1, 2, or 3 into the Jewel mall to see the famous HSBC Rain Vortex waterfall. If you have a short layover (less than 4 hours) or do not have the legal right to enter Singapore, you can still catch a glimpse of the waterfall by taking the Skytrain that runs between Terminals 2 and 3, which passes through the heart of Jewel without requiring you to clear immigration. However, to actually walk around the shops or the Canopy Park, you must officially enter the country.