This enormous red-brick church is the largest of its kind in the world. Its nave and 31 chapels can hold more than 20,000 people. The church endeared itself to the people of Gdansk in the years after the imposition of martial law in 1981, when members of the Solidarity trade union took shelter here. The sheer size of the church is just as impressive from the inside as it is from the outside. During World War II, it was severely damaged. Most of the walls were painted over in white, but some frescoes can be found behind the altar. Note the 500-year-old astronomical clock, dating from 1464, an oddity for a medieval Catholic establishment: It not only tells time, but also gives the phases of moon and shows the position of the sun and the moon in relation to the zodiac signs. There is a theater of figures at the top tier, which rotates at the hour. Also note the series of Ten Commandments paintings: The left side depicts the lives of commandment-abiding believers; the right side depicts the waywards. Climb the 402 steps to the top of the tower for an unparalleled view of Gdansk.