maniz is an adorable place with all the benefits of a large city and of a small town. It's close to Frankfurt, so it's very easy to get to. On the other hand, it has beautiful, quaint Fachwerkhuser archetecture instead of ominous skyscrapers, and it feels very safe, even in the early morning or late evening. Once the episcopal seat of the influential Prince-Electors, the "civilized" origins of Mainz date back to around 38 BC, when the Romans built a citadel here. The city's location at the confluence of the Rhine and the Main is ideal for trade, something reflected by the artifacts kept in the Landesmuseum, that show there have been settlements here since 300,000 BC! The most logical starting point is the Dom, or Cathedral of St Martin and St Stephan, especially on Tuesdays, Fridays, and Saturdays, when the farmers market is open.
Without doubt: Mainz has an impressive past. Sometimes the Roman relics give away the fact that it has a 2 000 year heritage, sometimes the magnificent baroque buildings remind one of the times of the Electors. The best architects and the most talented sculptors created the general character of the city in the 17th century and founded unique palaces for the nobility, as well as new churches.
You will miss a lot by not walking the city on foot: not only the archetecture and gorgeous statuary, but also all of the wonderful bakeries and butcher shops and the little details, like some little kid riding his tricycle over the cobblestones. The city has a wonderful, laid-back atmosphere. There are many pedestrian areas, and the street crossings are respected and popular. The streets tend to be windy, narrow, and irregular, so count on using the signs to find your way back to some sort of reference point. One thing you should watch out for are the cyclists... if you hear a little bell ringing, they probably want you to move to the side of the walkway
The Printing Press was invented in Mainz, and there is a museum detailing the development of the printed word, with tons of old Asian, Middle Eastern, and European manuscripts and a dozen antique presses. This Gutenberg Museum is cheap and worth a quick visit. All of the text is in both English and German. Following this theme, there also seems to be a higher concentration of book stores in Mainz than in most cities. A lot of people here speak English, especially in restaraunts or tourist destinations, but you will probably need some German if you want to communicate well in more 'local' places such as the market or the bookstores.
Another point of interest is the Cathedral. It's lovely and very interesting inside with lots of carved marble over graves. You could spend a few hours just looking at the sculptures, as they are very expressive. There are also occasional art exhibits in another wing of the cathedral. In the shadow of the Cathedral is the Market Place, which is a really charming, open square for most of the week. Some days there is an actual market abundant with fresh produce, and on the others you can just enjoy the statues. Throughout the entire city are many fountains and statues, from some modern art of a jumping man on a building near the Opera House, to a lovely fountain with fish jumping over balls, to egyptian style obelisks. There is also a beautiful well, the Marktbrunnen, which is the oldest of it's kind in Germany. Most of the Germans here seem to prefer eating foreign cuisine - apparently there is delicious Indonesian, Italian, Indian, or Chinese food to be found. The more traditional German food was incredible, though. Try delicous Pumpkin Soup.