There are enough monuments to ponder at in the Old Town:
starting with Johannes Gutenberg monument in Gutenberg Square
and Friedrich Schiller monument in Schiller Square
to a queer stone monument not far from Market Square (picture 5)...
These are some interesting monuments I have seen:
* Johannes Gutenberg, a great inventor;
* Friedrich Schiller, a great German poet;
* the Carnival monument;
* Little Bronze Soldier (I called it so);
* Queer Stone (a modern surrealistic monument, to make you think, too…).
The old historic center of Mainz was severely damaged in World War II, but has been beautifully restored. It's very walkable, and has a number of historic buildings and city squares.
The Marktplatz, or Market Square, is the real center of activity in Mainz. Surrounded by half-timbered houses, it has a gorgeous fountain in the middle.
Perhaps the most important building is the Electoral Palace, once the residence of the Archbishop of Mainz who was also the Prince-Elector. Completed in 1678, this is one of the finest examples of German Renaissance architecture.
Another outstanding building is St Peter's Church, built in 1748, a fine example of German Baroque architecture.
The largest Protestant church here is the Christ Church, with its elaborate Renaissance-style dome.
Kirschgarten, or the Cherry Orchard, is another quaint medieval town square. The orchard is gone, but the pleasant ambiance remains.