I was pretty well equiped (like 15 grenades and 80 assault rifle rounds) but I was being corned by three or four supermutant masters and had to go into the back of a nuka cola truck that had the exploding stroller. I survived, without any more ammo, no more drugs, and two dashes of health.
The other time was when I came across that baseball field near Big Town. I was walking up to it thinking' oh it looks just like the field I played at as a kid. I was level 2 on my first playthrough and still didn't understand how the compass thing worked so I was supprised when I got closer with the bodies suspneded from the fence and the raiders trying to kill me.
I have never gone into the Dunwich Building, after my friend told me how he had nightmares about the place two months after he went the I never had the guts to go in... I will some day though.
Edit: Also when I first went to Andale, I played through it perfectly without knowing what the place was all about. My friend told me to talk to the families, then the grandpa, then look in the basemant. I still get creeped out when I think about it. Plus I played it at midnight with all of the lights off and the TV as loud as it can go without the danger of blowing the speakers.