General comments:

Back on I'd Rather Be Surfing (see map). So that's where that locked door lead.

Monsters to kill:

Skitters and maybe the odd Ghast if you go looking for them

Decision to make:

You see a vine ladder going up. Ascending to Lasciate Ogne Speranza, Voi Ch'Intrate.
You see a vine ladder going down. Descending to Warning: Earthquake Zone.