What is the oldest cruise ship/ocean liner that is still in active service today?

[DenzelCrocker]

Just wondering. I've been fascinated these past couple of months about ships like the Titanic and the Lusitania, as well as the White Star Line (I think it stems from watching "Titanic' too many times). And by "in active service," I don't mean like a museum ship; I mean a ship that makes regular trips under her own power.