John of Nepomuk chapel, Religious chapel in Alsergrund, Austria

John of Nepomuk Chapel is a Secessionist central building designed by Otto Wagner and erected in 1895–1897 at Währinger Gürtel, arch 115, in Alsergrund. Its plan is a Greek cross: a circular domed shell with four short arms of equal length. The altars are in Neo-Renaissance forms, and the foundation stone of the earlier roadside chapel was reused for the new building.

A first chapel was built here in 1740 for soldiers guarding Vienna's outer fortification line; it was renovated and reopened in spring 1889, then demolished for the Wiener Stadtbahn embankment in 1892–1893. Otto Wagner designed the present chapel a few metres away, built 1895–1897 in Secessionist style, keeping the old chapel's foundation stone. It was his first sacred building in Vienna.

The chapel is run by the Verein zur Erhaltung der St. Johannes-Nepomuk-Kapelle, founded on 3 February 1916, which organizes benefit concerts, the Alsergrund street festival and maintenance of the building and organ. Since November 2000 the Verein Kulturbogen has also used it for lectures and discussions.

The chapel stands on the inner Währinger Gürtel at the level of Klammergasse, at Bogen 115 of the Stadtbahn viaduct, in the 9th district of Alsergrund. It is a rectory church belonging to the Alser Vorstadt parish and is a listed monument. The entrance faces the Gürtel, so it is reached on foot from the surrounding streets rather than from a tram stop in another district.

The chapel represents one of Wagner's earliest attempts to merge religious purpose with modern design language. This fusion between traditional sacred function and contemporary architectural thinking made it a showcase for his experimental approach to spiritual spaces.