I lived there for many years. It's a great place to visit for anyone. Try the pizza place -- it's fantastic!
It is a place to refuel.
I visited Hveragerdi three years ago. I found it a calm and mystical place, you just have to chill there! Walking is fantastic and there is a restaurant that uses underground thermal water to cook with, wonderful stuff. I have booked a flight for my sister to visit in May, but unfortunately cannot remember the name of the very cosy hostel we stayed at and unfortunately there appears to be no hostel there now.