Bastion 1 Hilsea Lines

The Victorian fortifications at Hilsea Lines are a proper window into 19th-century military engineering. This is serious defensive architecture - a series of earthwork bastions and gun positions built in the 1860s to protect Portsmouth from potential French invasion. Bastion 1 is the main accessible point, where you can walk the ramparts and actually see how the gunners would have positioned themselves. The whole complex stretches for miles around Waterlooville, but this section gives you the real flavour of what they were trying to achieve.

It's free to wander round, and the walk alone is worth doing - the paths give decent views across the surrounding landscape. Expect to spend an hour here if you're genuinely interested in the fortifications themselves. Family groups with older kids might find it engaging; younger ones will probably get bored once they've clambered up the earthworks once or twice. History buffs and military archaeology types will properly geek out over the gun emplacements and the engineering logic of the design.

If you're staying at one of the holiday parks on Hayling Island - and Kingfisher Caravan Park is only about five miles away - this makes a solid half-day excursion. The drive from Mill Rythe Coastal Village takes barely ten minutes. It's not a huge tourist draw, which means you'll have the place largely to yourself. Best visited on a dry day; the earthworks get muddy quickly in wet weather.