Conciergerie was a prison and known as the antechamber of the guillotine during the French revolution. This building looks quite powerful and has a tragical history.
One of its most famous prisoners was the French Queen Maria Antoinette, as well as the revolutionaries Georges Danton and Maximilien de Robespierre.

© Jorgefelix | Dreamstime.com
The whole building exists since the 10th century and was the palace of the Capetians. Conciergerie is located in the heart of Paris, in the district called “Ile de la Cite”.
Metro 4: Cite