(MONEY Magazine) – Bonneville Lock and Dam, Cascade Locks, Ore.; 541-374-8820; www.nwp.usace.army.mil/op/b; free. The oldest federal dam on the Columbia River and site of the state's salmon hatchery is just south of Mount Hood.

Buffalo Bill Dam, Cody, Wyo.; 307-261-5628; www.gp.usbr.gov/wy/bbr.htm; free. This historic 1911 Shoshone River dam near Yellowstone is notable for the scenic wilderness surrounding it.

Erie Canal, Lockport Locks & Erie Canal Cruises, Lockport, N.Y.; 800-378-0352; www.llecc.com; $11.50 for a two-hour boat tour (children four to 12: $7). The 363-mile canal connected the Hudson River to the Great Lakes.

Fort Peck Dam, Fort Peck, Mont.; 406-526-3431; www.nwo.usace.army.mil/html/Lake_Proj/fortpeck.htm; free. To create the four-mile-long earthen dam--the largest of its type in the world--builders dredged mud from the floor of the Missouri River.

Grand Coulee Dam, Grand Coulee, Wash.; 509-633-9265; www.grandcouleedam.org; free. This is the largest hydroelectric plant in North America and, at 550-feet high, one of the world's tallest concrete structures.

Raccoon Mountain Pumped Storage Plant, Chattanooga; 423-825-3100; free. This subterranean power plant pumps water from the Tennessee River Gorge to a reservoir 1,100 feet above.

Mississippi River Visitor Center, Rock Island, Ill.; 800-645-0248; www.mvr.usace.army.mil/missriver; free. The locks and roller dam, built in the 1930s to ease navigation on the Mississippi, are three hours from Chicago.

Soo Locks, Sault Ste. Marie, Mich.; 800-647-2858; www.saultstemarie.com; $16 for a two-hour boat tour. These four locks in Michigan's Upper Peninsula connect Lake Superior and Lake Huron, bridging the 21-foot gap in their water levels.

--JUDY FELDMAN