From the Marble Gallery, head right and up to reach the Outer Wall. This area is a vertical climb, filled with challenging enemies like Axe Armors and Medusa Heads. The double jump (Leap Stone) is essential here. Your main objective is to reach the top and activate another Teleporter, as well as find the Gravity Boots. The Gravity Boots allow Alucard to perform a super jump by pressing Up + Jump, which is necessary for reaching certain high areas.
Be wary of the numerous projectile-firing enemies. Use your shield and backdash effectively. There's a hidden room with a valuable item (often a high-tier weapon) accessible by breaking a wall near the top. Don't miss the Save Room located roughly halfway up the Outer Wall. Once you reach the top, activate the teleporter and proceed to the Clock Tower.