A giant gate. It is possibly this was inspired by the “Jurassic Park” doors seen in the movie. Possibly created by Rolf Mohr, as it was shared on his website.

Part of this model is currently lost. The doors can still be found in-game.

Source: https://web.archive.org/web/19991022053743/http://www.geocities.com/EnchantedForest/9057/Trespasser.html