Second Sunday in September is European Heritage Day. This means you can see the interior of buildings that are closed the rest of the year - like some private houses, cellars, the backstage area of the theatre. Other sights where you otherwise have to pay to get in are free on that day.
I've been in Freiberg on this special occasion two times so far and have enjoyed both visits tremenduously. Quite important is a proper plan for the day - go to www.tag-des-offenen-denkmals.de and choose your town, then pick whatever is of interest for you, print it out and map it out. Leave time for occasional chats with the owners of the buildings, unexpected discoveries (like a free guided tour of the Dom) and also for meals/coffee break.
Freiberg is rich of old townhouses, of architecture from past centuries. Not every townhouse is in a shape to be preserved, though. And we're living in the 21st century. It is inevitable that here or there a townhouse is torn down and someting new is built.
I'll admit here that I am not a fan of contemporary average architecture. Too often the cost of construction ranks first, quality comes second (if at all). Investors often have the "return of investment" in their mind, which translates to high profit as soon as possible.
I have rarely seen this in Freiberg. One example for modern architecture is right next to Cafe Hartmann, a few steps from Obermarkt into Peterstrasse. I remember that I saw a run down large townhouse there last time I visited. This time, in July 2010, it was replaced by a new building (a clothing shop) with an all-glass facade. Shocker. I am not a fan of that kind of architecture, it doesn't fit in the picture of this street at all. However, I went in and there was the next surprise: They had preserved the Gothic vaults on the ground floor. They were now right in the middle of the floor, integrated in the shop. So that was nice.
The construction of city walls started in the year 1200. Until the 17th century the city walls were constantly maintained and enlarged but between 1816 and 1877 large parts were torn down. Of the former 39 towers and five city gates are only nine smaller and one large tower plus one city gate (Donat tower and gate) preserved. The best preserved parts of the city walls are to see in the north near Schloss Freudenstein and the east (north of Donat tower).
Of the nine ponds outside the city walls are four preserved (north and west side). They are part of the gardens that surround the old town nowadays.
Freiberg's old town is very well preserved. Most townhouses you see were built after the fire in 1484 and re-designed/enlarged in the 16th century. Some are even older.
The first silver was found 1168 in the so called "Christiansdorf", now the lower part of the old town near Untermarkt square. In this area you find curvy, narrow cobbled alleys and smaller townhouses, former homes of craftsmen and miners. The character of the upper old town around Obermarkt square is different - orthogonal pattern of slightly wider alleys, lined with larger townhouses, often owned by Patricians, nobles and merchants in former centuries. Nowadays this is the area where you find most shops, restaurants, cafes etc.