On 7 and 8 September, a Europe-wide initiative opens normally inaccessible World War II bunkers, former concentration camps and relics from the German Democratic Republic.

Berlin’s turbulent modern history means it has more 20th-century monuments and memorials than most cities. While many are open to the public – including World War II bunkers, former concentration camps and various buildings connected to the former East Berlin surveillance apparatus – others are normally inaccessible.

But from 7 to 8 September, a Europe-wide initiative called the Tag des offenen Denkmals (Day of Open Monuments) is opening many of these sites to the public, including several from the Nazi and GDR (former East Berlin) era, as well as some controversial buildings that have polarised the city’s inhabitants. Visitors will have access to GDR relics such as Alexnderplatz’s squat, boxy Kongresshalle (used as a conference centre) and the tall, rectangular Haus des Lehrers (House of Teachers), an office building that still features a detailed communist mosaic by Walter Womacka.

The aim of the project, which is taking place in cities across the continent, is to sensitise people to the meaning of cultural heritage and interest them in the preservation of ancient monuments. The theme this year is: "Far away from Good and Beautiful: Uncomfortable Monuments?”

For WWII fans, the Olympiagelände (the former Olympic stadium area where Hitler held his infamous 1936 Olympics) and the associated Langemarckhalle (which contains 12 pillars bearing the 76 flags of the regiments that took part in World War I) will likely be a draw, as will newly opened spaces such as an air raid shelter on Stralauer Straße and a little-known forced-labour camp site next to the city’s biggest and newest park, Tempelhofer Feld.

Those interested in the Berlin Wall era will be fascinated by both the former Stasi Prison in Hohenschönhausen, which details how inmates were psychologically intimidated and physically abused, and by the abandoned former NATO listening station at Teufelsberg, a long-time Mecca for urban explorers that is usually only accessible via paid tours.

Admission to all memorials and monuments, some of which are staffed with expert guides, is free. You can find a full list of buildings on the official website, as well as details on how to register for the more popular tours and sites.

Paul Sullivan is the Berlin Localite for BBC Travel. He also runs/writes slowtravelberlin.com.

Correction: A previous version of this article incorrectly stated the date of the Berlin Olympics. This has now been fixed.