I really like the theme/melody of "The Mysterious Cavern." I think it suggests the title accurately enough.
"In The Depths" is inferior because each note sounds off predictably.
I have one suggestion for "The Mysterious Cavern." Chopoff those last few ascending notes after the 8 second mark. (Loading it in NoteWorthy, I see it's the last bar.) It sounds better when it loops if you do this. Example in attachment.
Awesome start, by the way! I hope to hear more stuff.