This beautiful building on the bank of the Main River used to serve as a customs house. It is also one of the oldest still standing buildings in Frankfurt. It was destroyed in WWII and restored recently. During its history, it has been restored several times and it is, therefore, a mixture of many architectonic styles. Now it houses a museum.
More information on Frankfurt's official website https://www.frankfurt.de/sixcms/detail.php?id=3793411&_ffmpar%5B_id_inhalt%5D=32392
Address Saalgasse 19, 60311 Frankfurt am Main, Germany
Coordinates 50°6'34.344" N 8°40'58.678" E