From the airport
The train runs directly from terminal 3, platform 2 to Copenhagen. It is a 2-minute walk from Copenhagen Central Station to the hotel.
If you take a taxi from the airport, it will cost around DKK 250,-. All taxis run on a meter and accept dankort and most major international credit cards.
From the Oslo boat
Take the train from Østerport Station (southbound). Get off at Vesterport Station. You can see Imperial Hotel from there.