1. The original title sequence from 1963 kicked off the episode.
2. Totter's Lane, where the First Doctor parked his TARDIS while his granddaughter Susan Foreman was at school, got a lovely wink at the opening of the episode.
3. And here's Coal Hill School itself, where companions Ian Chesterton and Barbara Wright taught. Look closely...
4. And we got a lovely little homage to TARDISes past via "the round things."
5. Although did you catch them again here, with Tom Baker himself?
9. The Doctor's phone number has stayed the same since Season 4's "Stolen Earth," at least.
11. The Eleventh Doctor actually carves the date and time of the first-ever episode of Doctor Who into the tower's wall.
12. And Clara drives past a clock displaying the time the first episode aired once more.
13. Clara's whiteboard at the start of the episode already had "no more" written on it.
14. The fez was, of course, quite present.
15. And these glasses sure do look familiar.
17. River's shoes are apparently a weapon of mass destruction worth keeping in the Black Vaults.
Not that this is actually surprising, come to think of it. Via.
20. Many of the Doctor's faces and Companions are visible on Kate's board.
23. The polarity got reversed.
25. Bummed you didn't get to see Hurt regenerate into Eccleston? Fans believe if you look closely at Hurt's right eye in this scene, it actually does morph into Eccleston's.
When the flames start to cover his eye, watch the eyebrow. Something definitely shifts.