Level: Dan's Crypt

On the right side of Dan's Crypt is a wall that looks brighter than other walls. This wall you can smash.

There are different ways to do it:

With a Club - first found in Level 3: Cemetery Hill. Jump down the left side of the mountain with rolling rocks to find the Club in a chest.

With a Hammer - obtained from redeeming 3rd Chalice in Hall of Heroes.

With Shield Bash - automatically unlocked after Level 5: Return to Graveyard

Once you got either one of these weapons unlocked, return to the first level "Dan's Crypt" and smash the wall. It takes multiple hits to destroy the wall. Behind it you also find a Life Bottle (Health Upgrade), which is great to have early on.