Bog bodies, which are also known as bog people, are the naturally preserved human corpses found in the sphagnum bogs in Northern Europe. Unlike most ancient human remains, bog bodies have retained their skin and internalorgans due to the unusual conditions of the surrounding area.
These conditions include highly acidic water, low temperature, and a lack of oxygen, combining to preserve but severely tan their skin. Despite the fact that their skin is preserved, their bones are generally not, as the acid in the peat dissolves the calcium phosphate of bone.
The German scientist Dr. Alfred Dieck catalogued the existence of over 1,850 northern European bog bodies in 1965, but many cannot be verified by documents or archaeological finds. Most, although not all, of these bodies have been dated to the Iron Age.
Many show signs of having been killed and deposited in a similar manner, indicating some sort of ritualelement, which many archaeologists believe show that these were the victims of human sacrifice in Iron Age Germanic paganism; though Cornelius Tacitus specifically describes bogging as a form of (sacralized) capital punishment in his 1st century work Germania. Some of the most notable examples of bog bodies include Tollund Man and Grauballe Man from Denmark and Lindow Man from England.
I saw some of these when I was in Dublin. They are fascinating close up.