The Beirut explosion should be a wake-up call to all of us, to store your Paper wallets and cold wallets in more than one geographical location. A national disaster or a accident like this might wipe out your house and if you used that as your primary hiding place, you would lose more than your house.
After a disaster like this, bulldozers are brought in and only the foundations might be left after they are done. (So hiding it in a safe or a wall or the roof is a bad idea.)
I believe hiding it beneath the ground will suffice. We must make sure that it is waterproofed, sealed, or laminated to prevent it from decay. I also agree that we should keep our private key in different places and should have several digital backed up stored in safe places.