Cahokia Heights, IL
Across the Mississippi from downtown St. Louis on the Illinois side. The Gateway Arch is 2nm NW; you can see it from short final. Built in 1929 as Curtiss-Steinberg Field, it was one of the busiest airports in the country during the 1930s — Lindbergh, Earhart, and Doolittle all flew here. The Air National Guard 126th Air Refueling Wing flew KC-135s from here until 2008. Today it's a Class D reliever for KSTL, popular with GA pilots visiting the Arch, Busch Stadium, and Cahokia Mounds (7nm NE, the largest pre-Columbian earthwork in North America). One of the great urban GA fields.
The 630ft Gateway Arch is the tallest man-made monument in the US — visible from 50+ miles in clear conditions. It marks the point where Lewis and Clark departed westward in 1804. Just 15nm north, the Missouri and Mississippi Rivers merge — two distinctly different colors of water flowing side by side for miles before mixing. Fly the river north from downtown St. Louis for both views. STL Class B airspace covers the downtown area.
The largest pre-Columbian settlement north of Mexico, just east of St. Louis. At its peak around 1100 AD, Cahokia had a population of 20,000+ — larger than London at the time. Monks Mound is the largest earthen structure in the Americas: 100 feet tall, covering 14 acres at its base. From the air, the geometric mound arrangement and the grand plaza are clearly visible. Most Americans have never heard of Cahokia — it's arguably the most underappreciated archaeological site in the country.
Bigger than New York's Central Park, Forest Park in St. Louis hosted the 1904 World's Fair and the 1904 Olympics simultaneously — the fair that, by legend, popularized the ice-cream cone and iced tea, and drew 20 million visitors. The grounds now hold the Saint Louis Art Museum (the fair's only major building meant to be permanent, designed by Cass Gilbert), the St. Louis Zoo, the Missouri History Museum, and the Science Center — all free. The park is a vast green rectangle just west of downtown, laced with lakes and the Grand Basin that anchored the fair's Beaux-Arts layout below Art Hill.
The most famous of Missouri's 6,400-plus caves, Meramec Caverns runs 4.6 miles into the Ozark limestone near Stanton, southwest of St. Louis. It's the one every Midwestern road-tripper knows from the barns: starting in the 1930s, the cave's owner painted "MERAMEC CAVERNS" on barn roofs across the country in one of the great American roadside-advertising campaigns. The cave itself has a genuine outlaw pedigree — Jesse James and his gang are said to have used it as a hideout, exploiting a hidden back exit. The giant "Stage Curtain" formation and the underground river are the showpieces; tours run year-round at a constant cool 60 degrees.