A locked gate under the sea
On the seabed, past the wreck, a gate bars a shaft that leads further down.
Nudge 1Where to look
It's rusty and solid. It needs breaking, not unlocking.
Nudge 2A stronger push
A heavy duty tool lies on the beach, on the far left.
What you needOther problems to solve first
Solve these first (each opens its own page, no answers on the way):
Show the solutionThe whole answer, with a video
Pick up the heavy duty rustproof pickaxe (beach, far left), dive to the gate and drop the pickaxe on it: the gate breaks open.