“ What if a invisible person could see other invisible creatures? All you would need to do to check for nasties hiding around is turn invisible.”
“ Whilst exploring underground the PCs discover tube like tunnels stretching for miles, upon further inspection the strange tunnels seem to connect all major cities in the are, what is their purpose?”
“ In a miltaristic nation, the ownership of proper (improvised don't count) weapons and armor is mandatory for all citizens under penalty of inprisonment or death.”