If we're keeping to strict definitions of tower, then I'd have to give a few honorable mentions.

Durlag's Tower from Baldur's Gate : Tales of the Sword Coast. One of my favourite dungeons in the series, which is saying something. It's also by far the biggest in the first game, with a wide variety of environments due to ~magic~.

Clock Tower from every Castlevania game ever. Medusa Heads. Still fun.

ADOM gives us the Tower of Elemental Fire. Fighting some high-tier demons in lava land is pretty cool, and "structured" levels in ADOM were rare.

Dark Souls 2 gives us the Brume Tower in the Old Iron King DLC, one of my favourite areas in the game due to its interesting visuals, tricks, and the best bosses in the game.