A woman in her 30s was allegedly sexually assaulted on South Common in Lincoln at about 6.30 pm on Tuesday while photographing the full moon and city skyline, according to Lincolnshire Police.
The force says the attacker struck her on the back of the head and dragged her to the ground. She escaped, called police and suffered minor injuries.
Investigators describe the suspect as a male about 5 ft 8 in to 6 ft tall, wearing a dark hoodie and jeans, with bad breath and a strong body odour.
A police spokesperson added that the assault likely occurred near the midpoint of the footpath that runs from Cross O'Cliff Hill to Canwick Road. Officers are asking anyone who was on South Common between 6 pm and 8 pm on Tuesday to come forward.
Police note no similar reports have been recorded in the area but acknowledge the incident may unsettle regular users of the common. Anyone with information should contact Lincolnshire Police, quoting incident 445 of October 27.