Ok, here's my game. It was not a terribly popular game at the time and I remember VERY little of it, so this is kind of a long shot. But a thread like this is probably my best bet!
Gameplay was MYST-like first-person, except instead of using pre-rendered scenes it used actual photographic imagery. It also used overlaid video to show movement in some scenes. You were able to turn and look around in 90 degree increments, again, much like MYST.
It was released in the 90's, probably 94-98, but I don't know precisely. It was definitely pre-2000, and I'm pretty confident it was post-MYST. Like MYST, it was one of those games where you were kind of dropped into a world and left to figure out what the game was about from there. I recall the game being very proud of its photo-realistic graphics. It was not a console game, it was either for Mac or PC - I had both during some of that time, and I'm not sure which I played it on.
There are only two parts of actual game play that I recall, and I believe both are fairly early in the game, but I'm not certain of that.
1) walking up (or perhaps down?) a hill along a dirt path. There were few or no trees, just grass on either side. It was a sunny day and everything was bright. Lots of nature, few or no man-made objects.
2) later on, there was a maze type puzzle. I want to say it was underground, but it was in stark contrast to the outdoor part. Everything was metal and I think it was some kind of transportation system, like a subway, but in a grid layout. (Thus, the maze)
I was a big fan of MYST et al and Journeyman Project, but I know it's not part of the MYST series, and after a bunch of googling I'm pretty sure it wasn't Journeyman Project either.
Ok, not a lot to go on, I know. But perhaps with some luck, nostalgia will be satisfied.

Feel free to ask clarifying questions. I'm unlikely to remember more, but you might spark a memory I can't recall now.