Yes, the HSBC Rain Vortex at Jewel Changi Airport is completely free to visit for both travelers and the general public. As the world's tallest indoor waterfall (40 meters high), it is located in the center of the Jewel complex, which is accessible without passing through immigration. You do not need a boarding pass or a ticket to view the waterfall from most levels of the "Forest Valley." However, while viewing the waterfall is free, some of the best vantage points are ticketed, such as the Mastercard Canopy Bridge, which allows you to walk right across the top of the vortex. The spectacular "Light & Sound" shows that take place nightly (usually between 8:00 PM and 10:00 PM) are also free to watch from the public tiers. If you are just transiting through Changi, you can take a free Skytrain between Terminals 2 and 3 that passes right through the Jewel, giving you a perfect (and free) elevated view of the waterfall without even having to leave the transit area.