The design of Cologne Cathedral was based quite closely on that of Amiens Cathedral in terms of ground plan, style and the width to height proportion of the central nave. The plan is in the shape of a Latin Cross, as is usual with Gothic cathedrals. It has two aisles on either side, which help to support one of the very highest Gothic vaults in the world, being nearly as tall as that of the Beauvais Cathedral, much of which collapsed. Externally the outward thrust of the vault is taken up by flying buttresses in the French manner. The eastern end has a single ambulatory, the second aisle resolving into a chevet of seven radiating chapels.
Internally, the medieval choir is more varied and less mechanical in its details than the 19th century building. It presents a French style arrangement of very tall arcade, a delicate narrow triforium gallery lit by windows and with detailed tracery merging with that of the windows above. The clerestory windows are tall and retain some old figurative glass in the lower sections. The whole is united by the tall shafts that sweep unbroken from the floor to their capitals at the spring of the vault. The vault is of plain quadripartite arrangement.
The choir retains a great many of its original fittings, including the carved stalls, which is made the more surprising by the fact that French Revolutionary troops had desecrated the building. A large stone statue of St Christopher looks down towards the place where the earlier entrance to the cathedral was, before its completion in the late 19th century.
The nave has many 19th century stained glass windows. A set of five on the south side is called the Bayernfenster, and were a gift from Ludwig I of Bavaria, and strongly represent the painterly German style of that date.
Externally, particularly from a distance, the building is dominated by its huge spires, which are entirely Germanic in character, being openwork like those of Ulm, Vienna and Regensburg Cathedrals.[