13. Mainz to Guntersblum

The base of the cathedral is a "column basilica" of Romanesque architecture with three naves (late 10th century), to which Gothic and Baroque elements were later added (17th and 18th centuries). It celebrated its millennium in 2009.
In the 10th century Willigis, Archbishop of Mainz, decided to build a new cathedral in Ottonian style.
Willigis had a "column basilica" built from the outset, with two choirs, two aisles on either side of the central nave and six towers. It was in the shape of a Latin cross and, because of its size, did not yet have a vault. The subsoil was still marshy due to the proximity of the Rhine, which caused problems with the foundations over the centuries.
The colours of the cathedral at that time remain an important field of research for the curator today.
Archbishop Adalbert I of Saarbrücken (early 12th century) had a two-storey Romanesque chapel erected adjacent to the cathedral, known as the Gotthard Chapel (after Gotthard of Hildesheim), as the princely chapel of the archbishop. As the warheads of this chapel are identical to those of the nave, it is possible that Albert was also the first master builder of the nave replacing Willigis's nave.
More information: Wikipedia

The Mainz Gutenberg Museum: In the centre of Mainz's Old Town, opposite the Cathedral, you will find one of the oldest book and printing museums in the world. Founded in 1900 by citizens of Mainz, the Gutenberg Museum is dedicated to the "Man of the Millennium" Johannes Gutenberg and his inventions.
Infos

The citadel of Mainz in Rhineland-Palatinate - Department of Mont-Tonnerre during the annexation to France - is one of the most beautiful citadels in Germany. In an excellent state of conservation, this tourist site gives the city of Mainz and its historic centre much of its character. The citadel is part of the Federal Fortress of Mainz.
Further information: Wikipedia

Nierstein is an important wine-growing community on the banks of the Rhine. The church is under the patronage of Saints Kilian, Colman and Totnan, Irish monks who evangelized Franconia between 680 and 689 and died martyrs in Würzburg in 689.
Wikipedia

Landskron Castle (Burg Landskron in German) also known as Reichsburg Oppenheim is a ruined castle located on a hill near the town of Oppenheim, Germany. Its first construction dates back to the 10th century. Its main façade faces south. It allowed the surveillance of the Rhine valley, visible to the south of the castle.
The castle was destroyed in 1118 and again in 1257 by the citizens of the town. It was rebuilt in 1244 and the castle and town were bombed by the French forces of General Mélac during the Augsburg League War in 1689.

The Katharinenkirche (Church of St Catherine) in Oppenheim, Germany, is considered an important Gothic building on the Rhine, alongside the cathedrals of Cologne and Strasbourg. Construction probably began in 1225, when Oppenheim was granted city privileges. Since the merger of the Lutheran and Reformed congregation in 1822, it has been a united Protestant church and its congregation is part of the Protestant church of Hesse and Nassau.

After the introduction of the Reformation in Guntersblum in 1608, the Catholic parish of the village probably held its services in Hangen-Wahlheim or Rudelsheim. The former Catholic church of St. Viktor, dating from 1101, was still used by the Protestant community. In 1617, construction of a new church began on the remains of the old building, which, due to the Thirty Years' War, was probably not completed until 1688. From 1697, the Catholics were granted the right to use the church in common, and a simultaneousousum was held. With the construction of a new Catholic church in Guntersblum, the further history of the Protestant church is considered separately.
From 1842 to 1845, the bourgeois community built a new church for the Catholics in the courtyard of the "Old Castle", which was also consecrated to St. Victor on 16 November 1845. It is a neo-Romanesque building with three high Romanesque windows and a round choir to the east.
More info at: regionalgeschiste.net