COPENHAGEN — Courtenay likes trains. I like the door-to-door convenience of cabs, especially when I’m tired.

Wherever we go, inevitably, there will be a small argument about the way to go.

It’s over now, though. There is only one way to travel, at least in Copenhagen: Harbor bus.

We caught our first one today, outside the Copenhagen library, a muscular-looking bright yellow boat that seated around thirty or forty people. We shared it with a group of five-year-olds out on a field trip, all of them snug in their Danish snowsuits. They ran to the back of the boat, gathering below the Denmark flag that snapped in the breeze, and stood gripping the rail and watching the boat wake as we sped north on the canal.

They loved it, and so did I, speeding the mile or two so up the canal to the stop at the Nyhavn wharf, outside the Danish Royal Playhouse, saving us another tiring 30-minute walk. There was sunshine and great views of the Opera House and other landmarks, there were no subway crazies, no surly cab driver, and no cost. The Harbor Bus is free with our Copenhagen Travel Cards.

We got off at Nyhavn, but all those kids stayed on board. The last I saw of them they were looking back at me, still gripping that back rail, enjoying the ride.

Portland needs a Harbor Bus.