Portsdown Hill
This is a fairly straightforward walk which can be tailored to what ever length you want. There are amazing views out over Portsmouth, Fareham, Langstone Harbour and the Isle of Wight.
Park at the viewpoint car park (Grid ref: SU 662 064) on Portsdown Hill. From here, go down the hill a little way and and walk to the right.
There are numerous paths running parallel along the hill. All quite rugged, but no steep climbs. Walk as far as you want along the hill then take another path back.
As you walk, you may spot a number of towers looking like the bridge of a warship. This a naval research base.
Along the top of the hill are a number 19th Century forts pointing inland away from Portsmouth. These were built to defend Portsmouth from possible land invasion. Never used in war, they are known as "Palmerston's Folly".
Fort Nelson now houses the Royal Armouries Museum. Well worth a visit, with free entry at the time of writing.