Gimme the katakana for those names and I can help. "Daemonth" and "Barbeth" come to mind for the first two, though Grohl for グロール sounds about right.
The first is literally "Firebreathing Mountain's Underground Cave." It doesn't use 火山, oddly enough; perhaps something similarly evasive instead of the obvious "Volcano"? Dragonmaw Cavern, perhaps?
The second is something like Mysterious Forest. I'd go with "Enchanted Forest" myself, given the other connotations of 妖 (妖精, 妖怪).
はらわた is 腸 - "Devil's Intestine." I want to call this "Beast's Belly" or "Belly of the Beast" (as in "Mark of the...", "...with seven heads and ten horns," etc.)
Then we have "Colt Plateau Waterfall Cave." I want to suggest a fantasy spelling like "Kolte" or something, but the rest of the name needs something snappy, too - maybe "Kolte Falls Cavern"?
You've got "Thousand Valleys" right, though it might be better to emphasize the range than the spaces between. "Thousand Spires," perhaps?
Same with the last one, though I'm still in fantasy spelling mode - "Port Malinn," perhaps.