“ When was the last time a character caught a cold or flu? Real people get them every now and again even with solid heating and dry interiors. Your characters are out in the cold and wet, and even inside is not always dry and warm. Imagine having to stop your dungeon crawl, sitting in a tight defensive position, while you all are feverish.”
“ 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?”