Towers are a staple in RPG- the high spires in the villain's castle. Or the towers where a final defense is mounted in a siege. Even in sci-fi, you have the skyscrapers and, to take it to an extreme, the orbital elevators that tie a planet to the stars. Usually, there is some reason that you have to fight your way to the top. Some incredible hard-fought (or over the top depending on genre) prelude to the final battle with the Big Bad high above the ground below, or to rescue someone important. Think Trinity and Neo in the Matrix, or Bruce Lee in Game of Death. It's a trope because it works- it's a way to communicate to players that this is climactic and should be treated as such, and this will get harder as you rise in levels- akin to levels in video games. How can we take this trope and turn it on its head?
1. The Big Bad is out for a meeting. Or something that takes him away from the location. Of course, you have to give the players something for the battle that they just waged to get there, but it doesn't have to be that final battle. This is especially true in more modern day scenarios where executives don't always stay put. 2. A fight from top to bottom. The only way to enter the sanctum is from the top- it is the least heavily guarded location in the big boss's domain. 3. Use of technology or magic to get around the trope. In our long-running Middle Earth campaign, after we goofed and Sauron got the ring, we were able to get a magic item that boosted the mage's power enough to teleport us directly into Sauron's tower. Of course, that didn't end well, but it was a different take. 4. The boss at the top isn't actually the boss, but a fall guy. This fall guy has some seemingly insignificant clue to the bad guy's location. (Make sure you have at least 3 ways to get this information in case your player characters aren't as fast on the uptake as you'd like)
What are some other ways that we can subvert the Tower trope?
Deep Blue Sea had a good twist to it. The sharks seem to be simply murderously going after the crew, who try to escape by fleeing progressively upward from the bottom of the floating sea station.
However, the real goal was that forcing the crew to flee would result in them opening doors to flood much of the station. This would lower the station enough to let them escape the cage.
Drawing inspiration from this, we could modify the trope such that the party is being manipulated to climb the tower. Whether or not there is a true "big bad" or treasure at the top is not relevant to the manipulator's plans. The true goal is something seemingly unrelated.
For example, maybe the manipulator just needs some chimera blood, and there just happens to be a chimera guarding the third floor latrine. The "big bad" at the top of the tower is just some random eccentric wizard whose research has nothing to do with whatever story the manipulator spun. By the time the party and the wizard figure what in the world just happened, the manipulator has gotten the chimera blood and is long gone.