St. Marien, Catholic church in Nordstadt, Bonn, Germany.

St. Marien is a neo-Gothic basilica of light tan brick with a dark slate roof, built 1887–1892 to a design by Joseph Prill. It measures 80 metres long and 20 metres wide, with a five-sided choir, two side aisles and a 77-metre tower with clock faces above the side entrance. Six figurative and two patterned windows came from the Schneiders and Schmolz workshop in Cologne-Lindenthal.

Joseph Prill, a religion teacher at Bonn's Oberrealschule, designed St. Marien as a neo-Gothic basilica. The cornerstone was laid on 14 August 1887, the church was blessed on 11 September 1892, and Archbishop Antonius Cardinal Fischer consecrated it on 7 November 1892 under the title of the Immaculate Conception of Mary and All Saints.

The church is dedicated to the Immaculate Conception of Mary and All Saints. Six windows with figurative scenes and two with graphic patterns were made by the Cologne-Lindenthal stained glass workshop Schneiders and Schmolz. The old pulpit now stands at the rear of the church.

The building is open on several weekdays with varying hours by season. Visitors should check current opening times before visiting and keep in mind that worship services take priority on Sundays and holidays.

The tower holds three bells cast by the Otto foundry in Hemelingen, made in 1951 and 1957 after a planned five-bell set was reduced for financial reasons. The largest strikes the hours from 7 a.m. to 10 p.m., and the Angelus rings at 7, 12 and 19 o'clock.