Disembarking cruise ship in Copenhagen . Spending 3 days before returning home . Where to stay. ? Central location to get most out of the 3 days. Day trip advice? Restaurants ?
Have you done any research, read any guidebooks or any one of the number of posts on this forum that asks these questions?
Do you have any special interests or concerns that might help people giving you a qualified answer?
Tivoli Gardens is a place that many people enjoy walking around, even if you're not into rides. Rosenborg Castle and gardens is high on many lists for things to do too.
Nyhavn and the Round tower
Nearby day trip (or maybe even less than a full day trip) is to Roskilde to visit the cathedral and Viking Museum there.