Kaiju Battle Adventure
Our heroes arrive in a large city being (slowly) obliterated by a battle between three extremely slow giant monsters.
Flail Snail vs. Gelatinous Cube vs. Roper
Underground Dwarf City slowly destroyed over weeks or months. Monster actions take hours.
Extremely avoidable, but causing major damage to infrastructure.
Treat like natural disaster, not combat
1000s of HP, AC 0.