There are plenty of tourism websites that go into great detail, including the Netherlands Tourism site, the Groningen Tourism site, and TripAdvisor. We have also made some suggestions for things you might do or see in and around the city.
The large church that dominates Grote Markt, Martinikerk, was first built in around 1230. But the tower dates from the 15th century. At the time, it was the tallest building in Europe. The two previous towers were destroyed by lightning, but the existing tower has weathered natural storms and numerous wars. Even today there is a bullet hole in one of the tower bells from the battle to liberate the city at the end of WWII. (You can climb it for stunning views of the city.)
Groninger Museum: If you came by train you will have noticed the post-modernist building opposite the station. That’s the Groninger Museum. An extremely varied collection: regional arts & crafts, oriental ceramics, postmodern design, neo-expressionist painting, and more. Museumeiland 1.
GRID graphical museum: Currently has an exposition of the work of the famous Groningen graphical art collective De Ploeg. Sint Jansstraat 2.
Nederlands Stripmuseum: Small, nostalgic museum exhibiting an extensive collection of vintage Dutch comic books. Westerhaven 71.
Shipping museum: Currently has an exhibition of historic stereo-photos of Groningen. Brugstraat 24.
University Museum: Includes the collection of Gerardus Heymans’ psychological instruments. Oude Kijk in ‘t Jatstraat 7a
The best way to explore the immediate area around town is by bike. Many bicycle stores offer bike rental.
Beachclub Kaap Hoorn: Here you can swim, have drinks, lunch, dinner, high tea more.
Verhildersum Manor and Estate: A beautifully preserved example of a typical Groningen manor. Take bus 65 from Groningen. Good way to see the country side too.
Lauwersoog: take bus 163 to Lauwersoog (about an hour) and see the impressive sea dyke, the mud flats behind it, the many birds, and the island of Schiermonnikoog in the distance. Leave early and you will have time to catch the ferry, visit the island, and get back to Groningen in the evening.
Leeuwarden, in Friesland: the European Capital of Culture 2018. Its Fries Museum currently has a beautiful exposition of the work of the graphic artist M.C. Escher. About 45 minutes by train.