Cycle races at a pro level are made up from one day classics, usually in the spring - races such as the 300 km Milan-San Remo, or Paris-Roubaix, which is famous for its mud & cobbles. You then have the shorter stage races, up to a week long, and then the big boys of Italy, France & Spain. La Vuelta is where Chris Froome came to prominence a couple of years ago, when poor tactics from Sky caused him to miss out on the win by a few seconds.
The one we've all heard of is the Tour de France of course, raced in July, with a huge global audience, and a 3 week tourist advert, with those amazing bucolic shots of the mountains, chateaus, fields of sunflowers...and it starts tomorrow!