Once you step outside and open that heavy door you'd be announcing to the world that you've awakened -- if the note Dr. Fielding left was accurate, you'd be a pretty tempting target for whatever creatures might be around. You thought it better to put that off for now and explore more of the bunker you were previously sealed in first to see if you can find other clues about what had happened in the three centuries you were asleep or if there's anything (or anyone) else here to find -- you hadn't seen anything else the first time around, but maybe a closer second look might reveal something.
Backpack with you just in case, you make a second search of the facility. It wasn't all that promising, though -- re-searching all the rooms didn't yield anything else in terms of supplies for a journey, apparently since you were pretty thorough the first time around. You did find a map indicating where other installations like this one were located in the area, though, so at least you knew of other places to check on and see if there were other human survivors currently frozen -- the landmarks and street paths in the city might be outdated, but it's a start at least.
You reach the last hallway you remember from your first look around and were about to turn around and write it off as a now-forever-unfinished part of the facility which the designers apparently never got to completing before a swing of your flashlight catches one part of the hallway weird at the end. Strange, was that doorway there before? You don't remember seeing that there the first time you were here, though that was before you got the emergency supplies and the flashlight. Maybe there's something there?