I haven't spent much time in Europe, as I like to travel more for nature and wildlife, but I have explored parts of the United Kingdom's more remote coasts as part of the expedition team for Noble Caledonia.
The United Kingdom technically includes the 'countries' of England, Scotland, Wales and Northern Ireland, and so these are treated separately. They collectively recently voted to remain separate from the European Union.
Some of the interesting parts that are technically part of the United Kingdom are some of the furthest flung islands in the world. All of these island groups have rare and/or endemic species to be seen. Considered the most remote inhabited islands is the Tristan da Cunha group. But I think even more remote are the Pitcairn Island group in the South Pacific. Of course one of the most controversial islands are the Falklands, where many species of seabirds, including huge Penguin colonies, can be viewed close up. For even more penguins there is of course South Georgia.