I ♥ the Oslo Fjord.

Although it's not technically a fjord like they have in the west, carved by glaciers -- with towering cliffs beside it.  In Norway, they tend to use fjord to refer to any large body of sea water.  The Oslo Fjord certainly is beautiful and accessible.  It's right there, in the city.  Oslo is so amazing for it's great mix of city and nature.  Take a short 15 minute bus or tram ride, and you will be in the woods and rolling mountains.  Very nice.