About 86% of Britons said the portrait, painted by Leonardo da Vinci in the 16th century, was a “let-down”.
The masterpiece hangs in the Louvre in Paris.
Checkpoint Charlie in Berlin, a crossing between the east and west during the Cold War, was the second most disappointing site, disliked by 84% of 2000 Britons polled.
The Manneken Pis in Brussels came third, with 80% unimpressed by the small statue of a naked boy.
The research by easyJet found that the Northern Lights were the most desirable experience in Europe, liked by 75% of travellers. Italy’s Lake Como was second most popular, with Greece’s Santorini third.