A popular walkers' bothy was attacked by vandals on Christmas Day.
Explicit images and words were daubed on and in Lingy Hut in the Lake District's Northern Fells, near the Cumbria Way.
One swear word was even painted on a sign urging visitors not to graffiti. A list of names and the date of Christmas Day was also scrawled on a bench.
Neil Stewart of the Mountain Bothies Association said it was "extremely annoying to put it mildly".
Volunteers will be sent to clean it up, he added.
Mr Stewart said: "It means somebody will have to spend some time and effort getting up there and rectifying it."
He said such attacks were rare but did happen "from time to time".
The bothy sits on the Cumbria Way and is one of 104 managed by the association.
It underwent a major renovation in the summer of 2017 and is a popular stopping spot for walkers.