The Opfermoor is an open-air museum. There is a separate museum about the place and the archeological findings nearby. The outdoor area is around a lake and has reconstructed houses and altars. It's a silent witness of ancient germanic culture. The place was a supra-regional cult site. It was used during the Hallstatt period until the 5th century CE. It's recommended to take the tour - I'm not sure if there is a tour in any other language than German. You've got to book a tour to make sure a local guide is around. There are signs to all of the builds which explain their former use (also German). The detail and ambience of this place is worth a visit. A Trip for both history and nature lovers. It's opened during summer. Announcements and prices are on their website.