Scotland for walking, The Lake District for walking and seeing the sights, beautiful country there. London for excitement and fun, the list is endless.
Buy a guidebook and look for what interests you and head for those areas ...... you really need to decide what you want to see because we don't know what interests you...if you want history for example you could find that almost anywhere, beautiful scenery then almost anywhere. If you want a mixture then you may find yourself confined to one county. how long would you be traveling here for? Again that will make a difference to what you choose to do.