A pub crawl is the act of visiting and drinking alcohol at a number of pubss in a single night with a group of friends. It's purportedly called a "crawl" because the carousers are literally crawling from pub to pub after getting initially soused after a few rounds at a few pubs. According to the OED, the term (including variations like 'gin crawl' and 'beer crawl') has been in use since the late 19th century. The pubs chosen for the route can be chosen according to a theme.