The fiestas of San Isidro are the most important fiestas of Madrid and honour Madrid’s Patron saint San Isidro. During the month of May there will be a number of events taking place, which include dances and fairs. The saint’s day is actually on 15th May and is a holiday in the city.
The fiestas of San Isidro are mainly associated with the bullfights that go on in the City’s bullring, Las Ventas. The bullfights which start on May 11th, and go on for over a month, are probably the most important (and best) that you will find anywhere in Spain. They attract the best matadors and, obviously, tickets are both hard to come by and expensive (though I did see some availabel on their website at reasonable prices).
The Plaza de las Ventas is a vast arena which can seat around 24,000 people and is considered the most important bullfighting venue in the world. It is a place where Spain’s ‘beautiful people’ go and you are bound to see the King of Spain, a famous actress or popstars, over the next month. An afternoon of bullfighting usually consists of 6 bullfights and can last a couple of hours. Two of the days will be dedicated to "corridas de rejoneo" – an amazing spectacle with bullfighters on horses.
Curiously, outside the arena there is a statue which is dedicated to Alexander Fleming, whose discovery of penicillin, has saved many a bullfighter over the years.
Tickets can be bought over the Internet (through Las Ventas website).