Jacob's Well

The water just drops straight down into blackness - that's the first thing that hits you at Jacob's Well in Sydenham. It's a natural sinkhole that's been swallowing water for centuries, though calling it a tourist attraction is generous. The well itself sits in a small park area, fenced off because people kept falling in, which rather sums up its appeal.

What you're actually looking at is a geological oddity - a shaft that disappears into the chalk below London, and nobody quite knows how deep it goes. The Victorians were obsessed with it; they threw things down to measure the drop and got wildly different answers each time. These days it's mostly locals walking past on their way to somewhere else, and the occasional geology enthusiast peering through the railings.

If you're camped at Lee Valley up in Edmonton, it's worth the trip south on the train for an afternoon if you're into that sort of thing - odd London landmarks that don't make it onto the postcard circuit. Don't expect crowds or facilities. There's nothing to actually do here beyond stare down the hole for five minutes and think about Victorians dropping stones into it. Families with young children might find it interesting for about as long as it takes to explain what it is.

Free to visit, no opening hours to speak of - it's just there. On a clear day you can see why early Londoners found it fascinating. On a rainy Tuesday in November, it's mostly just wet.