The main page claims that the adventure game Nightfall would be the first real time 3D first-person adventure and the page for that game repeats this error, because this is definitly not true!
The first game in this regard was actually "Under A Killing Moon" from Access Software:
http://www.legendsworld.net/AdventureLegends/1994.htm#568
This was a game which was groundbreaking in several other aspects as well, e.g. it should be also one of the first adventure games with FMV scenes and real actors.