Best-selling American author Dan Brown has officially opened a new Dutch library and museum devoted to rare esoteric books – the Embassy of the Free Mind – on Amsterdam’s Keizersgracht.

Best known for the ‘Da Vinci Code’, Brown is a big fan of the collection officially known as the Bibliotheca Philosophica Hermetica. Last year, he donated €300,000 to  help digitalise some of the collection’s esoteric books which inspired him.

Brown has studied at the library which includes some 25,000 books covering 5,000 years of western spirituality and was put together by businessman Joost Ritman. The collection includes very rare volumes on alchemy and medieval religious movements as well as works by Spinoza and Comenius.

Now located in the listed ‘House with the Heads’, the library aims to evolve into an international centre for stimulating free thinking.

Joost Ritman began the collection 60 years ago using the proceeds from his family business – which makes airline plastic cutlery – to fund it.

At the ceremony on Saturday, Ritman was presented with the Frans Banninck Cocq medallion for his services to culture from the Amsterdam council. Frans Banninck Cocq was a mayor of Amsterdam in the mid-17th century and is best known as the central figure in Rembrandt’s masterpiece The Night Watch.