Travincal is the name for the area in the center of Kurast City. It houses a few temples of the Zakarum and Mephisto's tower. It was the last surface area in Act III of Diablo 2. Nothing is known about Travincal in Diablo 3.
This is just part of the material available on this topic. TheTravincal article is available in the Diablo 2 wiki, which has a specific Diablo I and Diablo II focus. A lot of information unique to the first two Diablo games is available there. You can find it here:
- Diablo2.DiabloWiki.net/ .