Yes, Terminal 1 and Terminal 3 at Singapore Changi Airport are fully interconnected and very easy to navigate. Both terminals are part of the "main" airport complex (which includes T1, T2, and T3) and share a contiguous airside (transit) area. This means that once you have cleared immigration, you can walk between the two terminals or take the complimentary Skytrain, which connects the transit halls of T1 and T3 in just a few minutes. Additionally, both terminals are connected to the Jewel Changi Airport complex via pedestrian bridges. Terminal 3 is more spacious and modern, while Terminal 1 is known for the Aerotel transit hotel and its rooftop pool. Because they are connected airside, travelers can explore the lounges, gardens, and shopping facilities of both terminals regardless of which one their flight departs from, provided they leave enough time to return to their gate for security screening.