In The Calixcuel Incident, the Travellers are visiting an underwater city when a disaster causes it to begin leaking. Amid the chaos, they discover they have the means to save the entire city, if they can only reach and start the auxiliary reactor. However, the reactor is located in a secure bunker on the seabed, separate from the city, and between the Travellers and their destination are mobs of panicking citizens, jammed bulkhead hatches and several kilometres of ocean.

Not to mention the squid….