Remathilis
Legend
Agreed. For a megadungeon, Dungeon Delver is a must have feat for at least one party member.
For something like Hoard of the Dragon Queen, it may come up occasionally.
For a wilderness or political themed campaign it'll only come up as regret.
Thaumaturge.
The good news is: the earliest* you can take it is fourth level. By then, you should know what kind of campaign your DM is running.
* Well, unless you're an impulsive human. Then that's your own fault!