I'm sitting in a forest clearing, gazing out over a lake, my bike beside me as I munch my packed lunch. Sunlight plays on the water, and I'm alone bar the occasional jogger or family on a weekend stroll. The only oddity is a piece of crumbling wall daubed with graffiti reading: "Always remember." There's a wooden cross bearing 17 names nearby.
This incongruous sight is, in fact, a tiny part of what was the Berlin Wall, hidden in woods to the south-west of the city. I'm finding it hard to imagine this peaceful scene once cut through with stark concrete, watchtowers, floodlights and dogs.
As a child, I pictured the Berlin Wall as a straight line dividing east and west, and vaguely wondered why people didn't just walk along it and go round the ends. Years later I was glued to the TV coverage as the wall came down. But I'd never really grasped that it was a 160km loop, sealing West Berlin from East Germany. So, with this November marking the 20th anniversary of its demise, I decided to cycle the recently opened wall trail (Mauerweg), which follows its entire winding route.
You can cycle the whole thing, stopping off overnight along the way. But it's easy to combine a trip along one of the front lines of European history with some fun in one of the world's most exciting cities. The trail is in 14 signposted sections, with starting points easily reached by train or underground.
The trail starts in Potsdamer Platz, now the centre of reunited Berlin. With its sky-scrapers, it's more Starbucks than Stasi. More than 40km of wall ran through the heart of the city, but, with most Berliners intent on erasing evidence of its existence, little of it still stands. It's often tricky to visualise exactly where it ran, though a double row of cobblestones traces part of the route and at Checkpoint Charlie, the guardhouse has been reconstructed.
On Bernauer Strasse the full horror remains – with outer and inner walls and the "death strip" in between. At the documentation centre opposite chilling photos show how the barrier was thrown up virtually overnight in August 1961, and you can read incredible tales of desperate escape attempts. Further on, the watchtower on Kieler Strasse (of 300-odd, only two remain) is a museum to Gunter Liften, the first of many to be shot as he tried to cross the "anti-fascist barrier of protection".
Before long, though, you leave the tourist haunts behind, and find yourself cycling along the banks of the Teltow canal, across fields and woodland, with an occasional memorial reminding where you are.
At Alexanderplatz I put my bike on the train and head south to Wannsee, a picturesque lakeside suburb that just happens to be where the Nazis planned the Final Solution. Soon I'm pedalling through forests to Potsdam. The Glienicke bridge, where secret agents were once traded, glints in the sun, and the villas once used by Nazis, and where Winston Churchill stayed during the 1945 Potsdam conference, are now home to wealthy Berliners.
I arrive back in town in time to soak up some of 21st-century Berlin's vibe.
"You feel like a loser if you don't paint or play the guitar," my Berliner friend tells me. "Everyone's an artist of some kind."
He takes me to Prenzlauer Berg. I sip beer in An Einem Sontag im August (One Sunday in August), play babyfoot at nearby bar Nemo, and disco dance at August Fengler, with its retro flock wallpaper and glitterball. When I leave at 3am, the party's only just starting.
Next day I take the train north to Hermsdorf for a 15km stint. From the station, signs for the Mauerweg lead through suburban streets to a nature reserve. Swans and cygnets swim in a creek and there are pictures of animals you might spot along the way.
It's not far to the charming village of Lubars, with its cobbled streets, dinky church and banqueting hall, now a bar and restaurant with frescoed ceiling. It was a farmer from Lubars who reopened the road on 16 June 1990 by breaking through the wall with his tractor at Blankenfelder Chaussee – a plaque marks the spot.
Cycling on, I pass a lake that was partially filled when the wall was built and has now been restored. As I cycle through meadows along what was the border patrol road, Berlin comes into view in the distance, the Alexanderplatz TV tower piercing the skyline. I'm enjoying the ride so much I don't catch the train back from Wollankstrasse as planned, but follow the signs all the way back to Mauerpark, a green space in what used to be no man's land.
It's Sunday and the flea market is bustling. Performers busk on the grass, an electro beat echoes from a hidden party in the woods. At an outdoor karaoke session a young Berliner does her best Hannah Montana impression. On this sunny afternoon, the horrors of the past are a very distant memory.
• Lufthansa (lufthansa.com) flies from Heathrow to Berlin, from £98. Myer's Hotel (00 49 30 440140; myershotel.de) in Prenzlauer Berg has doubles from €140. For bike hire and wall tours contact 00 49 30 4373 9999; berlinonbike.de. Bikeline's Berlin Wall Trail (£10 from esterbauer.com) is a complete guide to cycling the trail, with maps and photos. For general information see germany-tourism.co.uk, and visitberlin.de.
