Secret passage to the Vault in the Wilhelm Watch. When you look closer, many tunnels and caves can be discovered. Hohentwiel is one of the largest and oldest castle ruins in Germany. The origins of the castle are in Hohentwiel 910 The castle was gradually expanded and served as Duke Castle. In the course of the 1600's. Century Hohentwiel was built to land fortress. In 1800 the fortress was left without a fight Napoleon's army. In the next six months, the fortress was made uninhabitable. Today, the fortress is an important tourist landmark in the Lake Constance region. In the castle there are countless attractive photo opportunities. To portray people the castle is a super location.