Witnesses said the photo shoot was held Friday at the entrance to one of the caves that give Cave Hill in Belfast its name, the Belfast Telegraph reported. One told the newspaper the woman, a blonde, was doing "typical glamour modeling poses -- nothing tasteful."
Some of the ramblers used their cellphones to record the scene and their shots ended up on the Internet.
One man said the woman caught his eye even before she took her clothes off because she was wearing a bright pink track suit and carrying a matching shoulder bag -- not typical clothes for an afternoon's hike.
"Even when people were walking up towards them, they didn't seem in any sort of panic to stop and the girl made no attempt to get her kit back on," another witness said. "It was blatantly obvious what was going on."
Nelson McCausland, the provincial social development minister, called for a city council investigation. He called the nude photo shoot "totally inappropriate."
Cave Hill, a major Belfast landmark, is important historically. There are remnants of a Celtic fort and cattle pen on the hill, the caves are old iron mines, and Wolfe Tone and Henry McCracken are said to have sworn loyalty there three years before the 1798 rebellion against British rule.