The idea is simple: heritage belongs to everyone, so once a year everyone should get to see it. Buildings that are normally closed - or that charge an entrance fee - throw their doors wide open. Some open their attics and basements. Some show their normally locked-up rooms. Some run special guided tours just for the weekend.
Each year has a different theme. One year it might celebrate a famous writer; another year, the country's railways; another year, traditional music. Buildings linked to that year's theme go all out - with displays, demonstrations and events. Schoolchildren sometimes get involved with class projects to share with visitors.
Families spend the weekend walking from building to building with a map of all the 'open' places. Long queues form outside the most popular spots. Children get a special passport-style booklet they can stamp at each place they visit. Some families try to visit as many as 20 buildings over the two days.
Día del Patrimonio started in 1995 with just a handful of buildings. Today, thousands open their doors across the whole country - not just in Montevideo, but in every town and village. It is one of the busiest, brightest weekends of the Uruguayan year and a way of saying: this story belongs to all of us.