I am thinking about going to the Harz Mountains and Goslar, but to be honest I know nothing about the region. How is Goslar? Is it a very expensive city? Is it worth visiting? Are the Harz Mountains impressive? Is the food in this region good? How is the weather in mid-august?
Goslar is a pretty looking, but quite touristy, city. I spent four days or so there last year, and that was too much. Most of the people visiting seemed to be 50+, or young families with children, although I can imagine it also being a very nice romantic destination to visit with a significant other. But as far as I could tell, I was the only backpacker there (the hostel I stayed at was filled with a schoolgroup and basically no one else). There were enough cheap eateries that I wouldn't classify it as a really expensive city, but being touristy, yeah, it's more expensive than other places.
The Harz mountains aren't "spectacular" in any way - they're just large hills, really - but there's some decent hiking around, various pretty lakes, and some castles on top of various hills that are worth a visit (I liked the one at Bad Harzburg - iirc).
The weather should be the same as everywhere in mainland Europe - warm (25-30 degrees Celsius) and sunny, except it could just as well be raining and only 20 degrees.
I know the Harz mountains quite well, as they are just right out of my backdoor. I've been there countless times - but never in the Goslar area. I live north of the Harz, so I know the northeastern side the best.
The highlights there are
- the Brocken
- several castles at Wernigerode, Benneckenstein, etc.
- the caves near Ruebeland
- the historic narrow-gauge steam train going up to the Brocken and connecting several touristic sites
The Lonely Planet Germany has some basic enough coverage on the area, IIRC.
The previous poster was quite right that it mainly an area that is visited by young couples and children and the elderly, all Germans. Not many international tourists go there - can't fathom why not, though.
If you are going, contact me - I might find the time to either help you a bit more with links and stuff, or accompany you as your own personal guide if you want to.
The Harz mountains are also a skiing area, btw - if there is enough snow.