Raziel first encountered one of these 'teleportation gates' in the Underworld at the start of Soul Reaver, where he encountered the first one in the Elder's tutorial in the Spectral Realm, as he proceeded through Kain's empire, Raziel was able to activate many other warp gates and was able to travel between them by selecting the appropriate symbol for each location and then stepping through. Each warp gate was marked with a blue 'sun' symbol on a door which led to the warp gate itself (the same symbol was repeated around the warp gate itself in green when activated) and a symbol specific to the location itself indicated which warp gate Raziel was intending to warp to.
List of Warp Gates
1. The Underworld - encountered during the Elder's tutorial.
2. The Lake of the Dead - located in the cave between The Sanctuary of the Clans and The Abyss.
3. Razielim City - set next to the stronghold's main coutryard.
4. The Necropolis - in the first tomb of the Necropolis.
5. The City - inside the Citadel.
6. The Silenced Cathedral - in the cave outside the Cathedral.
7. Zephon's Lair - on top floor of the Cathedral, just outside Zephon's nest.
8. Nupraptor's Retreat - on the platform located on the wall of the canyon housing the ruins of the Retreat.
9. The Tomb of the Sarafan - just outside the entrance to the Tomb.
10. The Drowned Abbey - in the corridor just outside the entrance to the Abbey.
11. The Lighthouse - in the cave next to the Lighthouse.
12. Ash Village - on the opposite side of the canyon housing the entrance to the Ruined City of Dumahim.
13. Oracle's Caves - in the entrance cave of the Oracle's Caves, before the cauldron.
14. The Chronoplast - just before the entrance to the Chronoplast.
It is unknown who constructed these machines but they appear to have an image of a specific territory with each individual gate. They may have been constructed by human slaves in Kain's empire (seeing as how the City has one as well, perhaps the Citadel was recaptured from Kain after a revolt) and there is also the warp gate in The Abyss caverns (how it got there is unknown).