Kayak
Access Staircase
In a kayak at the top of the access stairs to the fort. With the moorings released, he hurtles down the stairs and finds himself in the sea, to complete a course where he will find 3 baskets. He will have to tie these 3 baskets to a rope that his teammates will pull to bring them back to them.
The 3 baskets brought back, the team will be able to open the chest containing the clue thanks to the 3 small keys they contain.