Haslemere Charter Fair
Every two years, the town of Haslemere, England, holds a special fair, which has had it's ups and downs over the centuries.
There is this habit of it dropping out of sight every now and then, with reinstatements by various monarchs and dignitaries. Originally (1394) it was held annually, but since 1984 has been bi-annual. I attended the 2014 fair and enjoyed it.
The fair is part of the Haslemere Festival, which runs normally every year from mid May to the end of Junemainly around weekends. See more about that on: http://www.haslemerefestival.org.uk. There are a lot of events going on for that period of time.
The next Charter Fair takes place in the afternoon on the first Monday of May 2016. Thousands of people come to this. Train loads, bus loads, cars, etc-etc. The fair is not unlike Pamplona's Old Town Festival, which takes place yearly at the end of May. The crowds are about the same.
The 2014 Haslemere Charter Fair
There are a lot of stalls, with entertainment, parades and just general lightweight fun. You will find stalls from a wide variety of organizations, artisans, plenty to eat and, of course, the pubs have beer. It's primarily a family event and lasts for about 4-5 hours.
As with all such things, keep your valuables out of sight and safe from pickpockets.
Haslemere can be reached from London's Waterloo Station (catch a train around noon). Give yourself a good hour to get there and walk to the center of town where the Fair takes place (follow the crowds). Return as you came, it will be rush hour in London when you get back.
From around the middle of May through June you could attend some of the Main Festival events here, then proceed to the San Fermin's 9 day party.