Most beautiful I've seen is probably the entire portage between Turtle Pond and Clamshell Pond in the St Regis Canoe Wilderness... from the initial entry into a moss-filled evergreen forest at Turtle, to the sudden transition to hardwoods to the beaver meadow to the hillside paths and glacially dropped rocks on the hardest/toughest portion over the high part, to the gorgeous trek down into Clamshell with it's welcoming sandy beach and clump of purple pickeralweed right there, as well as the best place to sit for lunch to the right as you get there... it's just a gorgeous portage. I hate it and love it all at once.
Scariest thing I've ever had happen is a run in with a very angry and unleashed dog whose owners had the audacity to tell me "it's ok... he's just scared"... yeah, well so am I... and I'm carrying 75 lbs of wood/canvas that I would happily drop right on dear scared Fido should he venture a step closer. Seriously, what are folks thinking?
Oddest? A couple times I've found stuff at portages, like shoes, bags, sunglasses, knives, that sort of thing.
I did watch a pair of loons kill about a half dozen merganser babies right in front of me while eating lunch at the Low's Upper Dam portage, on Hitchen's Pond. This one washed ashore.
Another time, at the portage between Fish Pond and Little Fish, I watched some waterfowl ride this stream down, quacking and enjoying every minute of it, fly up to the other end, and do it again. Pretty funny.
And finally, this is something that's always puzzled me... at the "end of the line", as far back into the St Regis as you can go, is Lydia Pond... and there, at the camp site, someone decided that it was worth schlepping a few dozen bricks and some cement in to make a fireplace. Ok, probably it was brought in by snowmobile in the winter, but still... makes me wonder.