City Gate, formerly Büro Center Nibelungenplatz (known as BCN) and Shell Tower, is a 27-storey, 110 m (360 ft) skyscraper in the Nordend-West district of Frankfurt, Germany.

Büro Center Nibelungenplatz was designed by Novotny Mähner Assoziierte and part of the entire northern Alleenring comprehensive development plan, which provided for conversion to freeway and spot high-rises at all major intersections.

In 1993 the tower was renovated by Novotny Mähner Assoziierte, by cladding it in glass and equipping it with a panoramic lift.

Other tenants include the Frankfurt University of Applied Sciences, Merz Pharma, M. Page, Financial Times Europe, SCF, mediomind, REWE and a Subway restaurant.

City Gate was until 2013 a permanent shooting location for the ZDF television series Ein Fall für zwei (A Case for Two), because the lawyer's fictional law firm was sited in that building.