The Clock Tower is accessible from the top of the Outer Wall. This area is infamous for its numerous Harpies, Medusa Heads, and the constantly swinging gears. The Harpies drop their heads, which turn into Medusa Heads, making vertical movement tricky. Use your shield to block their petrifying gaze. The gears can be used as platforms, but timing your jumps is crucial.
Your primary goal here is to find the Spike Breaker armor. This relic allows Alucard to walk over spiked floors without taking damage. It's located in a hidden room accessible by breaking a wall near the top-right of the tower. You'll also need to hit four gears (two on each side) to open a path forward. Listen for the 'click' sound when you hit them. There's a Save Room conveniently located near the entrance to the Clock Tower from the Outer Wall.