Infinity Tower
The tower is an endless climb with a short cooldown between attempts, and its enemies scale on their own curve rather than on your level. That makes it the game's honest benchmark: your campaign progress does not help you here, so the floor you stop on is a fairly pure statement about your build.
How it works
Floors are fought one after another through the normal combat simulation, with a 10-minute cooldown between runs, which is short enough that the tower is an every-session activity rather than a weekly one. Reward quality is gated by depth, so climbing is worth doing even when the floor you are on is comfortable.
Best practice
When a floor beats you twice, stop attempting it. Two losses in a row is not variance, it is the floor telling you the build is short, and the answer is a stable floor farmed for gear or a dungeon run for an upgrade. The tower does not reset, so nothing is lost by leaving it for a day.
The common mistake
Re-running a floor you lose by a small margin. A near-loss feels like it is one lucky round away from a win, which is exactly why players spend an evening on it. The cooldown makes that expensive, and the margin usually closes from a gear upgrade rather than a re-roll of the same fight.