There are three hidden branches from the main path in this game.

The first one is in stage 3-1. There will be a point where you must descend a short vertical shaft. Halfway down here is a wall of pillars to the left. These can easily be demolished, where you will find a small side room containing hearts, cash bags, and some Roast.

The second secret, which is an actual hidden Block, is in stage 6-2. At the very beginning you'll need to pass a hallway with Axe Knights and falling chandeliers. The third archway has a chandelier but no guard. Hit the floor a couple of times and it'll crumble, revealing a stairwell into a secret area.

The last one is in Block 9-2. The third section has you jump across a bed of spikes at the beginning. After this you'll see several whirlwind tunnels and some coffins. The last upper platform on the right has a coffin and a tunnel. Let the tunnel suck you in and you'll find a hidden area full of bonuses.