The Zwinger was built between 1710 and 1728, by the architect Matthaeus Daniel Pöppelmann in co-operation with the sculptor Balthasar Permoser, as a great open stadium for festivals and tournaments, and as an orangery. It consists of six pavilions connected by large galleries, and I've seen it described as the most perfect example of late Baroque architecture in Germany. As originally built it was open on the north-eastern (river) side, as the money had run out for further construction, but the space was eventually filled in 1855 when Gottfried Semper built the gallery that lines one side of the square in front of his opera house.
At the south-eastern end is the Glockenspiel Pavillion, so called because of its carillon of 40 bells made of Meissen porcelain. Several guides promise that the carillon plays every 15 minutes, but they didn't do it for me (I later found a similar Meissen carillon in the Rathaus in Weimar, which sounded wonderful). In the centre now are four fountains, surrounded by shaped and manicured lawns. One of the best-known features, especially viewed from the outside, is is the Kronentor [Crown Gate], a baroque entrance topped by a large crown.
The weather was terrible for my visit: dark grey tending to rain.