This is very much explained by the title of the post, but perhaps could use further elaboration. On the original 1996 Tomb Raider game, it is possible to play some levels in almost-reverse order, avoid trigger points for enemies, and other such things.
In the last few years I’ve only played the version downloaded onto the PS3, which seems to lack some of the glitches of the actual PS1 version that make doing weird things like this possible (I still have the PS1 copy, but we haven’t unpacked the required consoles since before we moved house the last two times).
Some things are still possible though, and I do them quite a lot.
The best level for doing this is probably Obelisk of Khamoon, because you can access the required parts of the level quite easily in order to go the wrong way around. It’s also possible in Atlantis, and there is actually a doorway built into the level for this, probably so that game testers wouldn’t have to waste so much time ascending the pyramid. The action of jumping into the corner to cause the glitch though, is something I can’t get to work on the PS3 version.
With Obelisk of Khamoon, you can instantly glitch your way back into City of Khamoon through the railings, but it’s not much use for you to do so until you’ve got the artefacts you need. Some areas are just black and blocked off.
You have to go through the level in a normal fashion for a bit, until you are on the first bridge to one of the artefacts. From there, although you are not supposed to, you can actually make the leap to the left and onto a different bridge, instead of heading down to the water and then ascending via another room.
You can then do the other rooms in reverse and avoid the trigger points for the mummies.
So yeah, that’s something mildly entertaining you can do with the original Tomb Raider game.