My favorite part of the game is the exploration option and just stumbling across stuff.

Fairly early in the game, perhaps level 6 or so I stumbled across the Morning Star Cavern, and from that area you can basically do some lateral rock climbing and find yourself out on the large plateau beyond in the southwest part of the map. When I played F3, while I didn't exhaustively search it, but found that the line of the world map was pretty much the line of the world.

However with NV I found you can wander far beyond the map line. I climbed a long low mountain that was well beyond the line and looked out on this long rolling valley that went far off in the distance with a mountain range far away. I started going down it and there was no invisible fence that stopped me. Eventually I poked around in this really lonely landscape for a bit but eventually decided to just get back to the game as it was unlikely that I'd find anything hidden out there.

Is there anything out there? It's really cool that they made this solid buffer zone of "reality" before some final wall hits you, but it would be even cooler if there was something they seeded out there for those who really want to wander the wastes.

I have been there too, and haven't found anything. If you keep walking you wiil fall of an edge into endless water.