The arena in the Ruins of Lordaeron is the first to be set in a capital city (even though it's technically above the capital — the Undercity — and not accessible outside of speaking to the Arena Battlemaster). The Ring of Valor in Orgrimmar is the other arena in a capital city.
Although very similar in appearance to the Ruins of Lordaeron subzone above Undercity, the arena version has some notable differences. For one it is more symmetrical (one end doesn't lead to Tirisfal and the other to the throne room). Also, the Lordaeron Citizens are visible without the aid of invisibility detection, and of course in the arena they cannot be attacked. One of the most unusual details is that the arena is located on a map that is set not at Tirisfal Glades, but rather in Silverpine Forest. Players can only see the effects of this in-game through the mini-map, but an observant player might notice the road placement does not match up with that of the area around Undercity. In fact, the arena appears to have been placed in the same general location as Ambermill. Using an external map viewer application, one can see the roads to Hillsbrad Foothills and Greymane Wall, and even Shadowfang Keep. All of this is only an aesthetic effect however, and should not be interpreted as lore.