Deep in the bowels of a building, past the heavy door of the bank vault, is a secret tunnel under the Keizersgracht.

In the 1960s – when the canal was drained to lay cables – an extraordinary tunnel was built to link what were two bank buildings. It was not used for secret money transfer, apparently, but for high-ranking bank officials to go from the prestige office on the Keizersgracht for client meetings, back to the Vijzelstraat bank.

On Saturday morning a queue stretched around the corner of what is now the city archive to see this mysterious Poentunnel – blocked off 17 years ago and now open for Open Monumentendag weekend.

“Money tunnel, cash underpass, Keizers snip – the pedestrian tunnel dug between two old bank buildings on the Vijzelstraat has many nicknames,” said Amsterdam municipality in a press release. “In fact, the tunnel was hardly ever used to transport money. It was primarily bank directors who went discreetly through the tunnel from the car park under the Vijzelbank to the directors’ rooms in De Bazel…dry, when it was bucketing rain outside.”

Around the Netherlands, sites from the royal waiting room at The Hague Hollands Spoor station to an underground cinema in Amsterdam are open free of charge on Saturday 14 and Sunday 15 September.

Routes, networks and links

The focus this year is on routes, networks and links. In Groningen, visitors can ride an ancient route by horse-driven tram and historic bus. There are free tours of Evoluon, a former science museum built by Philips, in Eindhoven. The steam locomotive depot is open for tours in Rotterdam, amongst other activities.

In Utrecht, there are tours of the restored Maliebaanstation, opened in 1874 and used in the war years by the Nazis to deport Jewish people.

Although there are strict rules for owners of the 63,276 national monuments, they are also eligible for public subsidies for their maintenance. The annual open monument day aims to give the general public a peek behind their doors.