Saint John's Co-Cathedral is a baroque-style cathedral located in Valletta, the capital city of Malta. It was built by the Order of St. John between 1573 and 1577 and dedicated to Saint John the Baptist. The cathedral was designed by the Maltese architect Girolamo Cassar, who also designed other prominent buildings in Malta.

The interior of the cathedral is richly decorated with marble, gilding, and paintings. The nave is flanked by eight chapels, each with its own decorative style and theme. The cathedral also features two large altarpieces by the Italian painter Mattia Preti, who spent most of his life in Malta.

One of the most notable features of the cathedral is its floor, which is made up of around 400 tombstones that commemorate members of the Order of St. John. Each tombstone is intricately carved and decorated, and many are inscribed with the name and coat of arms of the person buried beneath.

The cathedral also houses the famous Caravaggio painting, "The Beheading of Saint John the Baptist". The painting was completed by Caravaggio in 1608 and was commissioned by the Grand Master of the Order of St. John. It is considered one of the artist's masterpieces and is one of the most important works of art in Malta.

Saint John's Co-Cathedral is a popular tourist attraction and a must-visit for those interested in art and history. It is also used for religious services and events throughout the year.