Bogs are marshy peatlands and acidic anaerobic environments. This lack of oxygen reduces decomposition where bacteria cannot survive and the acidic conditions act as a type of pickling juice preserving skin and hair although dissolving bones.

Bog bodies are thought to be sacrificial offerings, possibly kings and of Iron Age period (500/700BC - 500AD). However Cashel Man found in County Laois could date to around 2,000 BC.  But the oldest is Stoneyisland Man, Co. Galway whose skeleton mostly survived, unusually. It is over 5,000 years old but thought to be a drowning in an ancient lake that a bog grew over. 

Most of the bodies were young, of a certain status and showed signs of overkill - excessive wounds, hence the sacrificial theories. Old Croghan Man had manicured nails and wore a bracelet suggestive of high status.

There are more examples, I believe 17 in total - 9 men, 7 women and 1 child.

(unless stated otherwise the photographs were taken by myself)

Check out the following sites for more information:

Clonycavan and Old Croghan Men - Archaeology Magazine Archive

Kingship and Sacrifice | Archaeology | National Museum of Ireland

Ireland's Bog Bodies – Claddagh Design