Ambassador Transit Lounge (Changi T1)

Another non-airline affiliated lounge available in Changi Airport (T1). It is on the far end from the airline lounge area but on the same floor. This is adjacent to a free of charge cinema room (24/7) and next to this is the airport transit hotel, where you can have your own sleeping room for minimum 6 hours.
The lounge itself provides a gym, shower, and eat snack area. You can either pay for the entry or to enter by the Priority Card. PriorityCard covers the usage of
gym, shower space and eat & drinks.

Rainforest Lounge (Changi T1)

If you don't have the airline upper class lounge access, but do not mind paying some nominal fee or have the Priority Card, then you may want to try this one. With the priority card you have the free access of yourself, with usage right of Internet, shower facility and some light meal and soft drinks.