For instance around Swansea there is the famous Waterfall Walk at the Upper Vale of Neath (a dozen waterfalls in the space of two miles, from ten to ninety feet high because it is the confluence of four rivers - the Taff, Hepste, Pentre and Henryd; including The Gladys Falls, a curtain waterfall which is spectacular during the rainy season). At Ystradglynais the river disappeared into a large cave, reappearing a few hundred yards further downstream.
Then there is 3 Cliffs Bay on The Gower (avoid the Mumbles, full of adders sunbathing on the rocks according to a local I once met). It has stepping stones across a small stream. Beyond that is a small sea arch, a large sandy beach and a rock pool deep enough to bath in (a natural jacuzzi). The other side of the stream is a ruined castle on the hill and a marsh beyond (most people end up at the Worms Head but this is more scenic).
Beyond this is Tenby, with its quaint town walls and sheer cliffs - the start of a spectacular walk around The Pembrokeshire Coastal Path. You come to The Lattice Window first, an unusual rock formation, followed by Barafundle Bay, which you gain access to via a gate in a wall (nice sandy beach and grove of pines on far side). Bosherston Lily pools are beyond that, followed by Stackpole Head, with its collapsed caves, stacks and square window in rock. Finally you come to Castlemartin tank range with its dayglo tank, with the trio of The Elegug Stacks (two rock formations covered in a living white hair of seagulls, nesting there) plus chough colony on the mainland, where you view these from; The Devils Cauldron, a gigantic collapsed cave that if you lie down and peak over the edge, you can see the sea crashing on the rocks below. Lastly comes the Green Bridge of Wales, a rival to Durdles Door on The Dorset Coast.
Inland there is Pembroke Castle and Dan-Yr-Ogof show caves, the premier cavern system in Europe (also has dinosaur models outside): Wookey Hole near Wells, has more delicate stalagmite and stalactite sections (mini-cave systems) as does Cheddar Gorge.
The centre of the country has a ratchet and pinion train ride from Aberystwyth into the hills. It features The Mynach Falls at the Devil’s Bridge which Wordsworth visited and The Eagles Gorge, where Red Kites can be seen. Also central is Coed-Y-Brenin or the Kings Forest, the largest natural woodland left in Great Britain, if my memory serves me right (Scotland is all pines as is Thetford Chase and the New Forest is mostly scrub). Approaching Cadair Idris at dusk, it looks like some vast storm cloud approaching: If you are lucky you may see glow worms on the roadside (simply enchanting).
The North opens up via the railway journey over the Barmouth Estuary, with the sea full of seaweed below you. Beyond that is Portmeirion, where Patrick McGoohan’s TV series ’The Prisoner’ was filmed. Clever camera tricks made small buildings look large, on top of which there are stairs starting half way up a bell tower and other buildings that were just facades (beautiful!). Next comes the Blaenau Ffestiniog railway, up to the slate caverns at Llechwedd - spectacular in the morning mists. This is followed by an ordinary train trip to Betws-Y-Coed and The Fairy Glen (Swallow Falls weren’t that good in my opinion but apparently Victorian artists adored them). This is a dark, peat filled stream with pots, worn into the white rock, by water turning stones around, drilling holes into the surface (eerie looking). It is similar in appearance to the Eagles Gorge but easier to gain access to. There is also a legend associated with the area, of a knight killing a water horse at the bridge close by. In the vicinity is The Aberglaslyn Pass walk - an old road way you can walk along, that runs parallel to the main road above, giving good views of the small but attractive mountain range above.
Along the north coast is Conway, with its castle, town walls and railway bridge by Thomas Telford - again very attractive. There is also another ninety foot high waterfall close to the town, The Aber Falls which is easier to get to than the one at Swansea’s Waterfall Walk. Close to Llandudno are some interesting inland cliffs in layers, that resemble those in the Lake district. Also here are Bodnant Gardens, well worth a visit as far as landscaped gardens go.
The only places worth visiting in The West Country are around Tintagel, with its spectacular cave running underneath and St. Nectan’s Kieve, a small valley leading to a waterfall with a pot worn into the rocks below, from which the river spews out in a fracture in its side (enchanting little spot, named after a Celtic saint, whose sisters are supposed to have buried him in the river after diverting the stream). It is very similar to the largest waterfall in Wales, Pistyll Rhaeadr, in Llanrhaeadr-Ym-Mochnant (the valley of the pig) but not as high (maybe 20ft as opposed to 120ft). Again flowing into a pot and breaking out the bottom. This county also used to feature very accurately made buildings in its model village (Cornucopia) but alas it is no more. Also in this part of the country are the caves mentioned previously, Wookey Hole and Cheddar Gorge. Wiltshire has a spectacular drive at Longleat House, featuring a wealth of colour in May, when the rhododendrons, azaleas and other flowered trees and shrubs burst into bloom.
Scotland has the highest cliffs in mainland Britain at Cape Wrath (You may catch seals below, laying on a slab of rock and thinking that they look like maggots on a lump of cheese). On the North coast also is Smoo Cavern, which is the remains of a long sea cave, composed now of just a small cave with a boat tied at one end, where water floods in, in quite a spectacular fashion. Apart from this I think Scotland is overrated, just like Devon and Cornwall are.