Charro Days is the oldest continuously running festival in the Rio Grande Valley and the only one that belongs to two countries at once. It began in 1938 and has run every February since, taking over downtown Brownsville and crossing the river into Matamoros for a week.
What makes it unusual is not its size but its shape. Most festivals happen in a park. Charro Days happens in a city, and in two of them: multiple parades on different days, a rodeo, mariachi and marimba concerts, ballet folklorico, and street dances shared between Brownsville and Matamoros. The costume is the point — charro and china poblana dress is worn by people who are not performing, all week, in ordinary places.
If you have never been
Go for a parade and stay for what happens around it. The parades are the spine of the week and everything else hangs off them. Downtown Brownsville is genuinely busy — this is the week it is the busiest place in four counties, and a great many organizers elsewhere in the Valley plan their own events around not colliding with it.
Bring cash. Bring a chair if you are watching a parade.
If you are crossing to Matamoros for the Matamoros side of the celebration, check the bridge before you go — the wait is the thing that decides whether you make it.