B-b-but it's apocalypse proof!

bad photoshop in both idea and execution

its an artisanal cellar.

Once you add the underwater airlock in preparation for rising sea levels, it'll no longer be an issue.

Once the underwater airlock becomes a full-time essential feature, you'll get to test whether you properly installed explosive decompression preventions at high tide.

After that, you only have to worry about how much of your sand and bedrock the currents wash away.

Well you have to build your apocalypse bunker compound in a scenic area with a beautiful view, otherwise what's the point?

They are trying to sell a Shell out of Plastic which you burry in the ground

There are some shells you can get that you bury to make a cellar like this. Sand would be very easy to do this with. It would also be less efficient, pretty sure heavy soils make better cellars.

Maybe he needs further education with the story of the 3 little pigs.