Bedford River Festival

Takes place every two years. It's massive. It's the second largest outdoor festival in UK, smaller than Notting Hill Carnival but bigger than Glastonbury (though the performing artists are not A-list).
Free to attend so no tickets, no enclosing fence, but all the approach roads are closed off to traffic and these signs as you enter the festival site, which includes most of Bedford town centre. 
We sat outside with friends watching all the traders set up their stalls until midnight.