The street grid, the course of the wall, the location of the forum (Hohe Straße / Schildergasse) and the Capitol, the praetorium (town hall complex), the sewer system (including under the Kleine Budengasse), known outside cemeteries, glass and ceramic workshops; the Ara Ubiorum, the altar for Augustus and Roma (10 BC) is only suspected (at the forum). The city wall (middle of the 1st century AD), at least 7.80 m high, enclosed an area of 1 km 2, today’s center; it had 9 gates and 20 or 21 towers; the side gate of the three-part north gate is now (slightly offset) on Domplatz (the foundation in the Domparkhaus, middle section in the Roman-Germanic Museum). Further remains of the city wall can be found in Komödienstrasse and Zeughausstrasse, on the corner of Zeughausstrasse and Sankt-Apern-Strasse the Römerturm (former north-western corner tower of the city wall) with a mosaic of colored stones, southern parts on Rothgerberbach, Blaubach and Mühlenbach, western parts in the Sankt-Apern-Straße and the Mauritiussteinweg; South-east corner, so-called »Ubiermonument« from the beginning of the 1st century AD (included in the city wall around 50 AD). The paving of part of the street leading to the harbor has been laid (offset by 6 m) next to the Roman-Germanic Museum, which exhibits numerous ancient finds from Cologne and the surrounding area; the Dionysus mosaic (3rd century AD) is here in its original location.
The town’s landmark is the Gothic cathedral built on the site of a Carolingian-Ottonian bishop’s church: begun in 1248, completed choir in 1322, completed in 1842–80; Five-aisled basilica with ambulatory choir and chapel wreath, models are northern French cathedrals, especially Amiens. Monumental west facade with two 157.38 m high towers (plan around 1310). Excellent interior design: glass painting cycle of the 13th and 14th centuries Century in the high choir; largest medieval choir stalls in Germany (104 seats, around 1310); Gerokreuz (around 970); Milan Madonna (around 1290); Shrine of the Three Kings (1181–1230) from the workshop of Nikolaus von Verdun; Altar of the city patron, one by S. Lochner painted triptych (around 1440); Rubens carpets (1640); Funerary monuments and sculptures. The Cologne Cathedral, since 1996 UNESCO World Heritage Site, holds one of the richest treasuries in Europe. Two graves (woman and boy) of the Franconian nobility from the middle of the 6th century (perhaps members of the Merovingian king Theudebert I) were discovered in a small stone chapel (today cathedral treasury) under the cathedral.
Examples of industrial architecture include the Malakoffturm (1855) at the harbor entrance, the Wilhelminian-era platform hall of the main station (1890–94), the brick buildings of the former municipal power station on Zugweg (1883–1909) and the large Rhine bridges, of which the Hohenzollern railway bridge (1909–11 at the Place of a predecessor from the 19th century, destroyed in World War II, rebuilt in 1946–48 and 1957–59, expanded from 1986–89) is the oldest permanently installed bridge in Cologne between Dom and Deutz.
Cologne districts: In the suburb of Bickendorf, construction began on high-rise estate II in 1922, in which Riphahn played a major role. The main administration of the German health insurance in Braunsfeld was built 1967-70 by F. W. Kraemer. The development plan for the “Blauer Hof” (1926/27) and “White City” (1929/32) settlements in Buchforst was provided by Riphahn and Caspar Maria Grod. In the satellite town Chorweiler created G. Boehm a residential complex (1967-75). In Deutz there is the neo-Romanesque basilica Neu Sankt Heribert (1891–96) with the Heribert shrine (around 1160–70) and the exhibition buildings (1926–28) by Adolf Abel; in Dünnwald next to the Romanesque church of St. Nicholas (begun in 1118) the Kunstfeld settlement, the oldest surviving workers’ settlement (1820) in the Rhineland; in Ehrenfeld the Catholic parish church Sankt Mechtern (1954), a concrete skeleton building by Schwarz and the DITIB mosque (completed in 2017) by Gottfried and Paul Böhm. House X 1 (1961/62) in Hahnwald is owned by Peter Neufert spanned by a reinforced concrete shell. The event hall “Kölnarena” (since 2008 “LANXESS arena”) by Peter Böhm was built in the immediate vicinity of the exhibition stand. The university buildings in Sülz and Lindenthal were built with the collaboration of Abel, Riphahn, R. Gutbrod, H. Schumacher and P. Poelzig. The Catholic parish church of St. Laurentius (1961/62) was built by E. Steffann, the Church of Christ Resurrection (1967-70) is the work of G. Böhm, St. Mary Queen (1953/54) in Marienburg the last building by D. Böhm. Riphahn planned the “Grüner Hof” (1922–24) and the Nibelungen settlement (1919–28) in Mauenheim. In Müngersdorf there is also the residential house O. M. Ungers (1958/59) among numerous villas by important architects. In the district of Niehl are the churches of Alt Sankt Katharina (12th century) and Sankt Christophorus (1958–60) by Schwarz. On the outskirts of the residential area of Riehl, the Catholic parish church of Sankt Engelbert (1930–32), a rotunda by D. Böhm..