Where is it? On the Grand Union Canal Paddington Arm, about five miles west of Paddington station.
What's quirky about it? The quiet, rural-feeling canal is clearly at ground level - you think. But out of nowhere, the North Circular suddenly appears far below you: disorientated, you realise you're on an aqueduct.
Why bike there? The ride here from Paddington along the towpath is traffic-free and pleasant, going past Notting Hill. You might just see David Cameron or Madonna on a bike, but more likely some Polish blokes sitting on a bench with cans of lager.
Another six miles or so along the towpath from the aqueduct, go left into bustling Southall, whose High Street is more like India that west London. Eat fabulously and cheaply, buy delicious honey mangoes, and cycle back in a bargain sari. Or catch a train from back to Paddington.