The Clementinum, located in Prague, Czech Republic, is a historic complex of buildings that is home to the National Library of the Czech Republic. It is one of the largest and most beautiful library complexes in the world and is a popular tourist destination.

History:
The Clementinum was founded in 1556 as a Jesuit college and over the centuries, it expanded to include various buildings, including the Baroque Library Hall, the Astronomical Tower, and the Mirror Chapel. The complex was named after St. Clement, the patron saint of the church that used to stand on the site.

Tips for Visiting:
1. Guided Tours: It is highly recommended to take a guided tour to fully appreciate the history and beauty of the Clementinum. English tours are available and provide detailed information about the library, its collections, and the stunning architecture.

2. Baroque Library Hall: The highlight of the Clementinum is the Baroque Library Hall, which is an absolute must-see. Adorned with frescoes, gilded stucco decorations, and a collection of over 20,000 rare books, it is a sight to behold.

3. Astronomical Tower: Climb the Astronomical Tower for panoramic views of Prague's Old Town. The tower offers breathtaking vistas of the city's spires, red rooftops, and the Vltava River. Don't forget your camera!

4. Concerts: The Mirror Chapel, known for its beautiful acoustics, hosts regular concerts of classical music. Attending a concert in this stunning setting is a memorable experience.

5. Check Opening Hours: The Clementinum has specific opening hours, so make sure to check them in advance. It is also recommended to book your tour or concert tickets in advance, especially during peak tourist seasons.

6. Photography: Note that photography is not allowed inside the library halls and the Mirror Chapel. However, you can capture the exterior beauty of the Clementinum and the panoramic views from the Astronomical Tower.

The Clementinum is not only a significant cultural and historical site but also a place of immense beauty. Its stunning architecture, rich history, and breathtaking views make it a must-visit attraction for any tourist exploring Prague.