Aside of the cathedral the Old town in general is worth walking around in for a hour or two. Among the highlights are the city hall with the cannons in the little square opposite to it, Rousseau's birth house and various antique shops with all sorts of interesting stuff in the windows.
The new Espace Saint Pierre pass includes entrance to all three sites of Cour Saint-Pierre, a noteworthy space of unique spiritual and cultural importance. The Cathedral and its towers, originally Catholic, both embody the high point of the Reformed tradition and explore the origins of Christianity with an extensive archaeological site.
An underground passage, reopened when the Museum was created, connects the two buildings. The archeological tour beneath the cathedral is excellent for archeology fans it explains the origins not only of the cathedral but the reason for Geneva's location back to pre-Roman times. Those willing to climb the steps of the Cathedral's towers will be rewarded with magnificent views of Geneva and the lake.
When you visit the Old Town do not miss the International Museum of Reformation, located on the ground floor of the magnificent Maison Mallet (next to Saint-Pierre Cathedral), this new Museum presents the main spiritual and cultural elements of the Reformation. Unique objects, manuscripts, rare books and paintings illustrate the close ties between Geneva and the Reformation. State-of-the-art technology welcomes a modern audience: films, a music room, and demonstrations, including many for children, invite visitors to both rediscover the past and imagine the future.