An awesome idea would be a huge hollow planet that spins very quickly, the backstory would be that the core got so dense it became a mini black hole and swallowed most of the planet before being extinguished leaving a husk. The inside could support an atmosphere or even life and the outside could have very small (say 10-20 meter) holes that would lead to the inside. However there would not be many so the atmosphere would have a large pressure (say 2.5 atm.) the outside would be a black husk and the inside wouldn't be dark as you could incorperate glowing gas, or stones.
Another cool one would be a lava planet, you could code in a red ocean with a really low crash tolerance or you could incorperate the heating aspect, so your temprature would increase over time.