Adventures are practically made for speedrunning in this game. They're a great length, they have some variety and require some skill and routing (I think), and they're completeable in a manageable timeframe. They're even easily resettable. I'm already workshopping a speedrun for the first Adventure and I haven't even finished the other three.

There are some ruleset questions RE: which relics should be allowed. Assuming the ruleset permits arcanas, hyper, hurry, and (probably) random events, that provides a bit of a barrier to entry for main game progress as those would be a must. I don't think that's a big deal though.