Starting at Zeeheldenbuurt, Groningen, Netherlands, open the Explorial app and enter the 6-digit game code that you received by text and Viator chat message. The riddles take you straight into the heart of a city that has been doing things its own way since the Middle Ages. The first clue leads to the Martinitoren, the 97-metre tower that has dominated Groningen's skyline since the 15th century. Climb it for panoramic views over the city and the flat northern landscape beyond. From there the app takes you to the Groninger Museum, a deliberately provocative building sitting in the canal with its jumble of architectural styles — a museum that announces itself before you've even seen a single exhibit. Your final landmark is the Papengang, a narrow medieval alleyway threading between old buildings — one of the most atmospheric shortcuts in a city full of them. Allow around 2 hours. Groningen is very walkable, and the app guides you between landmarks with precision.