The centuries-old mystery behind a medieval passageway next to Paisley Abbey in Renfrewshire has now been solved.

Paisley Abbey Drain's intricate underground structure is believed to have carried material to the nearby River Cart, but until now no one has ever established where and how it met the river.

Following an eight-week dig over the summer, a team of archaeologists have painstakingly uncovered a well-preserved 14th century stone archway marking the exact point the drain and its contents once flowed into the river.

They found the tunnel - believed to be around 100m long - ends around three-metres from the banks of the present-day river, which would have been wider and shallower at the time the drain was built.

While the find is now being covered up again, the discovery could help lead to a more permanent visitor attraction opening up access to the drain in the future.

Dig leader Bob Will, of Guard Archaeology, said: "We found more than I was expecting and it is really exciting.

"We found the end of the drain and what was the boundary wall of the monastery.

"The main parts of the drain date back to the mid-14th century and are incredibly well preserved. It goes at least as far as the road in front of Renfrewshire House.

"Often these types of drains are in rural areas not urban ones where there will have been pressure on the land above it - but considering the amount of buildings on that site over the centuries, the condition of the drain is quite incredible."

The Abbey Drain Big Dig was co-ordinated by Renfrewshire Council and led by Guard Archaeology Ltd, funded by National Lottery Heritage Fund, Historic Environment Scotland and Renfrewshire Local History Forum.

More than 6500 people visited the dig, which also saw a strong community element, with volunteers from the local history forum taking part, and a series of events and seminars for residents and visitors.

The Abbey Drain has lain hidden for centuries until it was unexpectedly rediscovered in the 19th century, and in recent years, it has been periodically opened up for visitors.

There will be an opportunity for the public to put their names forward for a ballot to go inside it during this year's Doors Open Day in September.

Mr Will believes the discoveries of the past few weeks could help the development of a more permanent attraction.

He added: "What we have uncovered has helped us see what could be done with any future excavation.

"We now know much more about the medieval ground levels and have a good idea where some of the monastery buildings were.

"Ideally there would be more permanent access to the drain at some point in the future and what we've uncovered here makes that much more feasible."