Tidbits

1. In the level 'Alexandria', there are two posters on the wall. They are Egyptian movie posters. The left poster is the movie 'The Girls in Summer' (1960) and the right is 'The Time of Miracles' (1952). 
2. The Last Revelation was going to have an accessible diary feature, where Lara would write entries in about locations and the plot; hints and tips; maps and map fragments that Lara was to collect to give access to secret areas (PC only) and a scrapbook which would have had information on Lara’s past and her parents and of the previous Tomb Raider games.
3. The skeleton of Indiana Jones can be seen in the first training level, Angkor Wat. He can be found in the room with the spikes. 
4. The Snake Charmer that Lara activates in the level ‘Coastal Ruins’ has the face of Core Design’s co-boss Adrian Smith.
5. If you keep returning to Jean Yves in Alexandria after collecting a piece of armour, he will tell the player a new piece of information.
6. Kerry Shale is the voice actor for Werner Von Croy. In addition to Von Croy, he voiced many characters in TR4, TR5 and TR:AOD, such as Azziz in TR4 and Admiral Yarofev in TR5.
7. The corner bug was fixed by this game.
8. According to Richard Morton in 1999, there are a few goodies and challenges for the expert TR player. He also said that the designers had tried to get the rating for the game lowered, not by removing the blood but by having fewer enemies.
9. For the first time, Lara was able to switch between targets so that the player could choose who to take out first.
10. The grenade launcher was originally supposed to have smoke grenades.
11. There were two new moves that never made it to the game: shoulder barge and searching bodies.
12. Whilst returning through the same levels, you can go back and retrigger the secrets. There will be no items if you had picked them up previous but the sound will chime and it will add another secret onto your count.
13. The Mosque of Ibn Tulun features in the Cairo levels although it is bigger in reality than portrayed in game.
14. The PlayStation version of the game had it so that grenades fired by Lara or her enemies would deal damage to Lara if she was close enough. However, in the PC version of the game, Lara is immune to all grenade damage, including enemy grenades.
15. Poison arrows do work but they reduce the enemy’s health, they do not kill an enemy. The player must fire at the enemy again with any ammo other than poison to kill him.
16. There is a solution in the Lost Library for the fire snake puzzle, on a scroll. However, it cannot be picked up until the planetary puzzle is completed.
17. If you went around the fire snake puzzle pulling all levers counter-clockwise, the player would release a fire elemental. Completing the puzzle in any other way- including going around clockwise would mean that no elemental is spawn.
18. There is a hidden message in the game's executable file written by Richard Flower, who was a programmer for the game. It reads: “Tomb Raider IV - The Last Relevation -- Dedicated to my fiance Jay for putting up with this game taking over our lifes, my step sons Craig, Jamie & Aiden (Show this to your mates at school, they'll believe you now!!), also for my daughters Sophie and Jody - See you in another hex dump - Richard Flower”
19. According to issue 126 of the official PlayStation magazine which announced the PS4 version of Rise of the Tomb Raider, the total sales of Tomb Raider 4 on all formats is approximately 5 million copies worldwide.
20. According to issue 126 of the official PlayStation magazine which announced the PS4 version of Rise of the Tomb Raider, there were two PlayStation versions of this game; the first version allowed for up to five game saves and the title screen was triggered immediately upon death whilst the second version allowed for seven game saves.
21. In some PC versions, the Load and Save options in the inventory are displayed as images of PlayStation memory cards!
22. The first level with Professor Von Croy is a tutorial level where he will talk the player through Lara’s basic moves. However, it is slightly possible to move ahead of him, until the next trigger point. In some areas, it is possible to avoid some conversations altogether.
23. Lara’s boots change from being lace up boots in game to buckled boots in FMVs.
24. In the FMV where Lara and her guide are travelling in the desert on camels, there is a rattle snake (known for shaking its rattle). Rattlesnakes are in fact native to the Americas.
25. This game is the first in the series to include backtracking to previous levels. If the player picks up a secret in one level, progresses to the next level but then back tracks to the same secret in the previous level, the item will be missing, but the secret sound will be retriggered and the secrets counter will increase by 1.
26. In the Dreamcast versions of ‘Cleopatra's Palace’, there is a part where the player will step on a platform to trigger a golden Lara statue. However, this statue has a shorter plait than real Lara and she is also missing her guns.
27. In the tutorial levels, Lara’s voice sounds different, to match her younger age. However, if you try to use a secret, she will say no in her adult Lara voice. This is because the developers didn’t include a different ‘No’ sound file.
28. Lara Croft’s in game model contained 500 polygons.
29. The game contains 70 secrets over 35 levels.
30. According to Meagan Marie’s ’20 Years of Tomb Raider’, Von Croy’s appearance was based on Max von Sydow.
31. According to www.tcrf.net, fans have uncovered a variant Crossbow design, a shotgun with a flashlight attached and red flares. Fans have even found unused/ testing levels called ‘in the game files’ and these can be seen on Youtube.
32. In the PlayStation version of the game, Lara will leave footprints as she runs but this doesn't show in either the PC or the Sega Dreamcast versions.
33. In the Dreamcast version of the game, Lara has a more human shaped shadow that does in fact change size depending on where the light source is in that particular room.
34. The character models of Jean-Yves and Werner Von Croy were created by a US company called ‘Viewpoint’. Core Design commissioned them to create 3D medium to high resolution models using the rough drawings and facial photographs that they provided. First they built sculptures before digitalising them, complete with textures, skeletons and morph targets for the animation process.
35. If you use any medipacks through the inventory (rather than a hot key), you cannot use more than Lara needs when her health is already full.

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Sources

No. 01
Alexandria Movie Posters ~ SLAYER on TRF 
https://www.tombraiderforums.com/showpost.php?p=4944739&postcount=7

No. 24
Rattlesnakes in Egypt
http://web.archive.org/web/20010422061751/http://www.larasmansion.freeserve.co.uk/nitpicks4.htm

No. 32
Lara’s Footprints
http://web.archive.org/web/20010803171225/http://www.larasmansion.freeserve.co.uk/nitpicks0.htm

No. 33
Lara’s Shadow in Sega Dreamcast
http://web.archive.org/web/20010803171225/http://www.larasmansion.freeserve.co.uk/nitpicks0.htm

No. 34
Viewpoint Commissioned Character Models
http://web.archive.org/web/20001011220648/http://tombraiders.com/Archives/Dec_5_99.htm
https://web.archive.org/web/20000510023120/http://www.viewpoint.com/about/resume/games.html