But with all these hills, valleys, lakes and coastlines to choose from, where do you start? Well, all 11 of the national parks in England and Wales (there is none, as yet, in Scotland) have an education service designed to point teachers and pupils in the right direction on field trips.
Funded mainly by central Government, services vary from park to park, with each tending to concentrate on its strong points. So you might find that the Lake District's education officer could tell you everything you ever wanted to know about mountains, the North York Moors would be the experts on heather moorland and the Pembrokeshire Coast would have everything ship-shape and Bristol-fashion when it comes to the coast.
Steve Drinkwater, education services officer for the Pembrokeshi re Coast,says: "It's natural for us to concentrate on our specialisms. But we try to tailor the service we provide to individual schools' needs".
In Pembrokeshire this could vary from half-day guided walks around the coastline with a ranger, to an evening lecture wherever the school group is staying.
One of the feathers in Pembroke's cap is the award-winning reconstructed Iron-Age settlement at Castell Henllys, near Newport, where the school's programme ties in with the requirements of the national curriculum. Here children can dress in Iron-Age costumes, learn how to weave and spin, and even indulge in spear-throwing competitions, while learning about life in Britain 2,500 years ago.
A similar programme based on life in Elizabethan times is also being developed at Carew Castle near Pembroke, which the park leases from the owner.
"We are fortunate in having these two unusual sites within the park," says Mr Drinkwater. "But with some of the most impressive coastline in Britain we can also provide advice on more traditional field studies.
"Indeed, we have a remit to promote an understanding of the special qualities of the national parks. If children pick this up early it helps them appreciate their natural heritage as they get older, and perhaps even work actively towards conserving it," he adds.
This is echoed by David Brinn, education officer for the Brecon Beacons National Park. "We've recently started to develop initiatives aimed at educating for sustainability," he says. "One of these is our Sustainability for Real project, where junior schools go through a role-play scenario based on land use planning. We pretend they're in an environmental forum where they have to make decisions on developing a wind farm, a recycling centre and a car park, or passenger minibus service".
The park has also developed a biodiversity project, in co-operation with Brecknock Wildlife Trust and Powys County Council. Twelve participating schools within the old county of Breconshire are to study the biodiversity of their local area. Each will adopt a pond or river, as well as a woodland and a hedgerow for one term, and not only study them for their own sake, but also look at wider, related issues such as how water resources are used elsewhere in the world.
The local wildlife trust has also provided the schools with a list of species it wishes to monitor as an additional part of the project, which it designed to last 10 years - so it's possible that some of the first students working on it could be administering the project as park employees before it runs its course.
All the national parks are keen to develop close ties with local schools, and it is common to see rangers in the classroom or out and about with school groups. But they have no priority over schools from outside the parks. Rangers will also help groups interested in practical conservation work such as tree-planting or footpath maintenance.
There are three residential study centres within the national parks - Losehill Hall in the Peak District, Plas Tan-y-Bwlch in Snowdonia, and Danwynallt in the Brecon Beacons. These are more involved with training programmes than educational courses and field study projects, and are in the vanguard of conservation and planning studies.
Before visiting a national park on a field study course it is worth getting in touch with its education service - even if you have no plans to use it directly, as staff can provide a wide range of specific resource material. Mr Drinkwater advises contacting them at least six weeks before you visit. He says: "Our services are always pretty stretched, but by giving us plenty of time to respond, you'll be sure of getting all the information you need.
THE 11 NATIONAL PARKS OF ENGLAND AND WALES
* Brecon Beacons National Park,
7 Glamorgan Street,
Brecon, Powys LD3 7DP.
Tel: 01874 624437
* The Broads Authority,
Thomas Harvey House,
Norwich, Norfolk NR3 1BQ.
Tel: 01603 610734
* Dartmoor National Park,
Parke, Haytor Road,
Bovey Tracey, Devon TQ13 9JQ.
Tel: 01626 832093
* Exmoor National Park,
Dulverton, Somerset TA22 9HL.
Tel: 01398 323665
* Lake District National Park,
Windermere, Cumbria LA23 1LJ.
Tel: 01539 724555
* Northumberland National Park,
South Park, Hexham,
Northumberland NE46 1BS.
Tel: 01434 605555
* North York Moors National Park,
The Old Vicarage,
Helmsley, York Y06 5BP.
Tel: 01439 770657
* Peak District National Park,
Derbyshire DE45 1AE.
Tel: 01629 816200
* Pembrokeshire Coast National Park,
Pembrokeshire SA61 1PY.
Tel: 01437 764636
* Snowdonia National Park,
Gwynedd LL48 6LS.
Tel: 01766 770274
* Yorkshire Dales National Park,
North Yorkshire DL8 3BP.
Tel: 01969 650456