The Secret Zone is the last hurrah on the planet! So this is how to clear Beacon Beach Secret Zone!
PLANET KEY
Did you get the Planet Key yet? You need it to open the Secret Zone. Solve 7 Side Quests at Beacon Beach and buy the key at the Robot Rabbit Shop.
THE ENTRANCE
North west, left of the Lighthouse on the map, there is a path you can take, down to the base of the Lighthouse. There are some closed pipes and a yellow cube just next to the pipe that you can pick up.
Carry it south along the beach until you see a device in a little alcove to the left. Put the cube in here. This will open up the white pipes. Use them, climb up the ladder to the other side and fight the Darkmess.
Now all the Mess is gone, you see a colourful door. Climb down the ladder,open the door with the key and go through.
THE SECRET ZONE
You’ve entered the Secret Zone and you’re standing in front of the exit / entrance. Go around the corner and use the white rabbit pipe.
At the top, work your way down. Again as in the screenshot, from red dot to yellow dot.
And from there further down (red to yellow).
Continue your way down until you see the Spark. But there is some Darkmess with a green triangle shape that we need to get rid of first.
Take the ladder down and from there further downwards.
Go through a small tunnel until you see the green triangle shape lying on the floor.
Pick it up and carry it all the way back to the ladder. The device for the green triangle is on the same level as the ladder. Put it inside.
Now the Darkmess disappears and you can climb both ladders up to meet the Spark.

This is MARIO AND RABBIDS: SPARKS OF HOPE
Release: October 20th, 2022
Developer: Ubisoft Milan and Paris
Publisher: Ubisoft
Official Website: https://www.ubisoft.com/en-gb/game/mario-rabbids/sparks-of-hope
Guides by camzillasmom.