Floor by Floor, Oozing Right up to the Door

Unaware and indifferent to the fact that it’s losing ground on its prey, the brainless, gelatinous, green mass continues to advance onwards and upwards until it’s finally stymied by a barrier with gaps too narrow to easily ooze through.
The simple but pragmatic act of reblocking the three-foot-thick, ‘Lord Urdurel’ cold-iron door, probably saved the lives of at least half the Party.