On the edge of Loviisa's city center, you can find the Loviisa earth fortress and the bastions of Rosen and Ungern. The site is free to visit and open year-round.

In 1745, the town of Degerby was founded at the head of Degerby Bay, and in 1752 it was renamed Loviisa in honor of Queen Lovisa Ulrika. To protect the town, a fortress was needed.

Construction of the Loviisa earth fortress began in 1748, led by Augustin Ehrensvärd, who also designed the Suomenlinna fortress off the coast of Helsinki. The fortress was meant to surround the entire town, but only a small part of the plan was completed.

Nearly finished were the bastions Rosen and Ungern on both sides of the King's Road, along with the earthworks associated with them. The bastions were named after Finland's then governor-general G. Rosen and General von Ungern.

During the Finnish War of 1809, the fortress was taken over by the Russians and lost its military significance as the border moved far to the west. The fortress began to ruin, and the inner courtyards of the bastions gradually became grazing land and vegetable gardens. During the heyday of spa tourism in Loviisa in the 1890s, the fortress area was rediscovered for recreational use.

The fortress has been restored multiple times by the Finnish National Board of Antiquities. The latest restoration of the ruins was completed between 2006 and 2012. In late summer 2008, a historical nature trail was opened around the fortress area through a collaboration between the City of Loviisa, the National Board of Antiquities, and the Porvoo Museum.

The Ehrensvärd Trail provides visitors with information about the fortress construction, cultural history, as well as plant and animal species, through signs placed in the landscape. In addition to the two-kilometer forest loop, there is also a shorter and more accessible route.