Torksey Viaduct

The viaduct straddles the River Trent just outside Retford like some Victorian engineering flex that time forgot to demolish. Built in 1875 for the Great Northern Railway, it's a proper red-brick showpiece - twenty arches of the stuff, each one a testament to when railways mattered and builders took pride in making them look good.

You can walk underneath it, which is free and takes about ten minutes either way depending on how long you dawdle. The scale of it only hits you when you're directly beneath the arches - way more impressive than photos suggest. The brickwork's weathered but solid, and there's a nice bit of towpath alongside where you might spot a heron if you're lucky. Don't expect queues or facilities. This isn't a visitor attraction in the modern sense - it's just a bridge you can appreciate for what it is.

It appeals most to railway enthusiasts and walkers tackling the Trent Valley way. Kids get bored after five minutes unless you're into that sort of thing. Families staying at nearby Trentfield Farm or Wild Acre Village could easily work it into a morning walk, especially if the weather's decent.

Going in spring or autumn works best - less mud than winter, less chance of melting in summer. Sundown Adventureland is close enough that you could combine it with the viaduct on a quieter afternoon. The real value here is that it's free and genuinely interesting if Victorian engineering does it for you.