Created in 1917 by the Army Corps of Engineers, the locks (known locally as the Ballard Locks) link saltwater Puget Sound with freshwater Lake Union and Lake Washington. All day, every day, a passing parade of yachts, barges, fishing trawlers, and other vessels make their way from one body of water to the other. And people line the shore to watch, wave, and maybe wish they had a boat of their own. Exhibits in the Visitor Center explain how this engineering feat came about and was executed (water levels in the lakes dropped about 17 feet as a result). If you want to glide through the locks yourself, take the Locks Tour offered daily by Argosy Cruises. On the hill above the locks you’ll find the Carl S. English Botanical Garden, well worth a stroll. Over a 43-year period a botanist named Carl S. English, Jr. transformed the once barren grounds into, in his words, “a garden worthy of serious study.” The garden is filled with unusual trees and shrubs; there are more traditional flower gardens down behind the Visitor Center.