Dig Up the Sea

Now this gave me the idea for a weird item.

Magic item, Shovel of the Deep Sea, extremely rare

This shovel enables its wielder to dig through water as if it was solid ground. Tunnels and chambers digged with this remain for up to 24 hours, after which the water returns to its normal state. When shoved into the "ground" at the entry of a chamber created with it, the shovel suspends the countdown until it's removed, causing the countdown to pick up where it stopped (e.g. when placed in the entryway 3 hours in, and removed 6 hours later, 21 hours would remain until it collapses). While its duration is extended that way, the entry of the tunnel at the surface is magically camouflaged and hard to spot.

Otherwise, it works and looks like an ordinary shovel.

This is just an idea, so tweak it to your liking if you want to use it in a story or something, or to make it more balanced, if you like this idea.

Let your creativity run wild ^^