The best part of the 1980s video game Pitfall was exploring the underground caverns. The game was extremely two dimensional where you progressed through the jungle starting on the left side of the TV screen to the right and then you’d appear back on the left in a new part of the jungle. When you finished the game you could reverse your journey, going right to left and exploring any unentered passageways.
I recently discovered the app video game Dear Esther, which has a similar linear direction where you walk back and forth around an island. I was hoping for secret passages, underwater caves and such, but it was only a mono-realm, alas.
What video games have you enjoyed that had multiple realms, hidden rooms or alternate dimensions?