Johanneum Gymnasium

New building at the Speersort

In 1826, a new school building was ordered but initially not implemented due to a lack of funds. Construction took place from 1838 to 1840 at the Speersort location, the site of the Hamburg's old cathedral which had been demolished in 1806. This is where the Hammaburg stood, the nucleus of the settlement that was to become the city of Hamburg. The medieval St Johannis monastery was demolished at the same time. The imposing classicist new building, designed by Carl Ludwig Wimmel (1786–1845) and Franz Gustav Forsmann (1795–1878), consisted of a main middle building and two wing structures that were connected through arcades facing Domstrasse, where the main entrance was located. The building was based on competing designs by Alexis de Chateauneuf (1799–1853) and Carl Ludwig Wimmel. The building survived the Great Fire of 1842, which caused numerous buildings nearby to go up in flames, including St Petri church.

The Speersort building housed the two schools (Gelehrtenschule and Realgymnasium) as well as a library that later was to become the city's public university library (the Staats- und Universitätsbibliothek) and a higher school for academics ("Akademisches Gymnasium").

New Maria-Louisen-Straße building

In 1914, the Johanneum moved into what is today the building complex designed by Fritz Schumacher on Maria-Louisen-Strasse, while the old Speersort building was used entirely by Hamburg's public university library at the time. The Speersort building was largely destroyed in the bombing raids on Hamburg in 1943; the remains (including a surviving part of the arcades) were removed for widening the streets in 1955 (the foundations were uncovered again in 2005 during archaeological excavations on the former cathedral square). The entire complex of the Johanneum in Maria-Louisen-Strasse with the Schumacher buildings has been a listed building since 1979. The Bugenhagen memorial created by Engelbert Peiffer in the courtyard has been a listed building since 1958.

In 1948, three years after the end of the Second World War, a group of students from the Johanneum visited London. Frederick Wilkinson, the headteacher of Latymer Upper School, believed that only getting to know young people can bring about understanding, reconciliation, and thus lasting peace in Europe. In this spirit, he initiated the student exchange that has taken place every year since then, and which has been extended to other schools and countries.

It has an important historical library that is also open to research.

Individual girls in the upper classes were admitted earlier, but it was not until 1977 that the first girls were enrolled in sexta.

Forum Johanneum

The Johanneum has received a large new building through the donation of millions by a patron. It is a three-story building with a total area of 2200 square meters, which contains art and music rooms, a cafeteria, a theater rehearsal room, and a sports hall. The Forum Johanneum was officially opened on May 24, 2007, as a new building.

On the south facade, there is an inscription in ancient Greek. The inscription translates to: "All people naturally seek knowledge" and is a quote from Aristotle's Metaphysics.