The history of the Beelitz-Heilstätten began in 1898 when the Landesversicherungsanstalt Berlin (the state insurance institute for Berlin) bought an approximately 140-hectare parcel of woodland from the town of Beelitz.
The lung clinic and sanatorium first built there with a capacity of 600 beds received its first patients in the spring of 1902.
Over the following years the land covered by the sanatorium complex more than doubled in area and was extended to include over 60 buildings.
Adolf Hitler recovered here from injuries sustained during the First World War and Erich Honecker was treated for liver cancer before fleeing to Moscow in 1991.
In 1945 the Soviet Army appropriated Beelitz-Heilstätten, which became the largest Soviet military hospital outside the Soviet Union.
Like many of the buildings in East Germany controlled by the Red Army, the sanatorium at Beelitz has stood empty since the withdrawal of Soviet troops from the Germany in 1994.
Over the last 20 years Beelitz-Heilstätten has been a favourite of urban explorers and photographers drawn by the strange beauty of peeling paint and nature reclaiming the land.
The opening of the Baumkronenpfad in early September 2015 is the first step in a plan Heilstätten Projektentwicklungs GmbH has to attract visitors by landscaping the parkland and making the abandoned buildings accessible to the public.
The walk over the treetops starts with a 36-metre climb to the top of the main viewing platform. From there you overlook the 23-metre high walkway that extends for 320-metres to the ruins of the old Alpenhaus.
This is just the first incarnation of the Baumkronenpfad, which will in time be extended to 1000-metres.
I was taken aback by the length of the queue when I visited around noon this past Saturday, which meant a wait of about 15 minutes and the queue had more than doubled in length by the time I left about 2 hours later.
The combination of sunshine and the colourful leaves of trees displaying their autumn finery made for a spectacular sight.
Entrance to the Baumkronenpfad costs 9.50 EUR for adults, 7.50 EUR for children aged 7-17 and is free for children up to 6 years old. As well as viewing the buildings from above a 1-hour tour including a history of the Beelitz-Heilstätten and a quick glimpse into the Surgery Pavilion is available for 4 EUR. Photo tours in the Alpenhaus and Surgery Pavilion with go2know cost 10 EUR per person.
You can check opening times, find directions from Berlin and get more information about the project on the Baum & Zeit Baumkronenpfad Beelitz-Heilstätten website and Facebook page.