Madison Square Garden is a well-known indoor arena located in Midtown Manhattan, New York City. It has been the home of numerous sports teams, including the New York Knicks and Rangers, as well as hosting many high-profile events, such as concerts, circuses, and political conventions.

The nickname "the world's most famous arena" has been attributed to Madison Square Garden for several reasons. First, it has a long history of hosting significant sporting events, such as the first-ever NCAA basketball tournament and several heavyweight boxing matches, including the "Fight of the Century" between Muhammad Ali and Joe Frazier. The venue has also hosted many iconic musical performances, such as The Beatles, Elvis Presley, and Michael Jackson.

Additionally, Madison Square Garden is located in one of the world's most recognizable cities, which adds to its notoriety. The venue has also undergone multiple renovations and upgrades, ensuring it remains a state-of-the-art arena for spectators and performers alike.

While some may argue that the nickname is subjective, it's fair to say that Madison Square Garden has a rich history and reputation that has earned it the title "the world's most famous arena" among many sports and entertainment fans.