So, the gates are built by the minerals and whatnot.
There's something I still don't understand though, and I couldn't find any reference to it on the wiki. When you select a gate to join/start a party, you can see the potential levels you might get on each depth, but is there some way of knowing what level you'll get when? (aside from the random graveyard/treasure levels). There's some cryptic arrowheads, what do these mean? If it shows A->B->C-> does that mean that the next group to go through will get A, and then the group after B? Or does it change at a set time?