The tower is infinite, but follows certain rules. Here is what to expect on your climb:
Mostly you will encounter common enemies. However, there is a 30% chance for a random event.
Every 3rd floor (3, 6, 9, 12...) an Elite enemy lurks. These are much stronger but often drop Relics.
Every 10th floor (10, 20, 30...) a powerful Boss awaits. You are fully healed after victory.
After every 3rd floor, you have the option to visit the Merchant to spend your Gold.
An encounter instead of a fight: gold for HP, a relic, a card or a wager. Some outcomes cost you Max HP for good.
Reachable before every even floor. The barkeeper sells a potion; there is also dice and arm wrestling for gold.