The Last Vacation

From publisher blurb:

The characters, normal humans on vacation, fall prey to a natural disaster that traps them beneath a hotel. Here they struggle to find a way out, fighting the elements of the disaster: flaming gas jets, flooding water, poisonous chemicals in the air, and collapsing debris. Clearing a passage they think leads to the surface leads them into the secret underground facility of the Mindhead, a super-intelligence from another dimension. Mindhead’s facility is damaged and the leaking cosmitronic energy incapacitates them, leaving them on death’s door.