The Midsummer Fire Festival is represented relatively equally in all capital cities, so you don't need to worry about the entire Azerothian population being packed into Ironforge and Orgrimmar. Below is a list of where, exactly, the festivities are in each of the capital cities.
- Stormwind - Just north of the Mage District, west of the Trade District. Next to The Stockade.
- Ironforge - At the far back of the city, in the Hall of Explorers.
- Darnassus - Outside of the city proper, in Rut'theran Village, right by the dock to Auberdine.
- Exodar - In the center of the Crystal Hall, the northmost wing of the city.
- Undercity - Above ground in the courtyard, right by the city gates.
- Silvermoon City - In the Court of the Sun, just outside of Murder Row.
- Orgrimmar - In the Valley of Wisdom, just outside of Thrall's chambers.
- Thunder Bluff - On the Spirit Rise, near the northwestern edge of the bluff.