The Doctor's attempt to give Harry a trip in the TARDIS sees the two of them and Sarah arriving onboard a space station in the far future, with some rather deadly security mechanisms.
Did You Know?
When the Doctor and Harry first discover the room full of cryogenically frozen humans, there is a point where the two of them are talking and, from over Harry's shoulder, you can see one of the "frozen" humans opening and closing his eyes. See more
This is a sterile area! Keep out!
Just like hospital.