The pair, who've been dating since September, spent an afternoon visiting the famous Pere-Lachaise cemetery.
Gosling, 31, and Mendes, 37, enjoyed red wine and Argentine fare before visiting the resting places of Jim Morrison, Édith Piaf and Oscar Wilde.
An observer told People.com: 'They were holding hands and there was a lot of tenderness between them.'
From Pere-Lachaise, they continued their grisly tour at the historic Catacombs of Paris, where visitors can go below ground to see the ancient stone quarries that make up the ossuary, housing the skeletal remains of approximately six million Parisians.