By car via E6 / E18 Mosseveien or E6 from the north:

Follow the E6 towards Oslo city centre until you see a sign with the ferry symbol and the names 'Copenhagen' and 'Fredrikshavn'. From there you will be led up to the big roundabout over the E6. In this you keep left, turn off at the exit that displays signs with the ferry symbol and keep following them. You will then pass the new Opera House on the left and the big pink harbor on the right.

By car via the E18 Drammensveien:

Follow the E18 towards the city centre, past Hjortnes/Color Line and down into the Festningstunnelen. There is a exit for the Tempel River on the right hand side just before the end of the tunnel. The exit has a ferry symbol. When you get out, keep to the right and follow the signs.

It takes 15-20 minutes to get to the terminal from Oslo city center on foot. If you stand with your back towards Oslo S (railway station) and look up towards Karl Johans gate, you will turn left towards the red building called 'Oslo Havnelager'.

You then cross the E18 over one of the bridges. From here you will be able to see the ship at Vippetangen and follow the signs marked 'walkway to the ferries'.