As of my last knowledge update in September 2021, the Colosseum in Rome, Italy, offers various types of tours, including the Colosseum Underground and Arena Tour. However, please note that details might have changed since then, so I recommend checking with official sources or tour operators for the most up-to-date information.

The Colosseum Underground and Arena Tour typically offers visitors a more in-depth and immersive experience of this iconic ancient amphitheater. Here's what you might expect from such a tour:

1. Access to Restricted Areas: This tour often grants you access to areas that are not part of the regular general admission, such as the underground chambers beneath the Colosseum's arena floor.

2. Arena Floor: You may have the opportunity to step onto the arena floor itself, where gladiators and other performers once battled. This provides a unique perspective of the Colosseum's interior and allows you to imagine what it was like during its glory days.

3. Underground Chambers: Exploring the underground areas of the Colosseum can be a highlight of the tour. These chambers were used for various purposes, including holding animals and slaves before they were released into the arena.

4. Historical Insights: Knowledgeable guides often accompany these tours, providing historical context and sharing fascinating stories about the Colosseum's history, architecture, and events that took place there.

5. Smaller Group Size: To enhance the experience, these tours usually have smaller group sizes compared to regular admissions, allowing for a more personalized and interactive tour.

6. Duration and Tickets: The duration of the tour and specific inclusions can vary depending on the tour operator and ticket type you choose. Some tours might also include access to other nearby ancient sites, such as the Roman Forum and Palatine Hill.

7. Reservation: Due to the popularity of the Colosseum and limited availability for these tours, it's advisable to book your tickets in advance. You can often purchase tickets directly through official channels or authorized tour operators.

Remember that guidelines, pricing, and tour options may have evolved since my last update. For the most accurate and current information, I recommend visiting the official website of the Colosseum or reaching out to official tour operators in Rome.