The Great Medieval Drain is a vaulted subterranean structure outside Paisley Abbey dating from the medieval period.
Extending to a length of about 90m, this finely crafted stone-lined 6ft high conduit supposedly took waste material from the Abbey complex to the White Cart river.
In perfect condition, the navigable section – which was discovered in the early 1990s during an archaeological dig – is accessed via a surface manhole cover.
The archaeological investigations of the 1990s also unearthed a wealth of objects including rare specimens of organic material such as wood, leather and plant remains.
Carved slates, some of which exhibit the earliest written polyphonic music discovered in the country, and the largest assemblage of medieval pottery recovered from any site in Scotland were also discovered.