Old Route 66 followed today’s I-270 around the north side of St. Louis, crossing the Mississippi River on the restored Chain of Rocks Bridge, but one of southern Illinois’s biggest attractions sits directly east of the Gateway Arch, off the I-55/70 freeway at exit 6. Clearly visible to the south side of the Interstate, the enigmatic humps of Cahokia Mounds State Historic Site are the remains of a city larger than London was in AD 1250. Over 100 earthen mounds of various sizes were built here by the indigenous Mississippian people while Europe was in the Dark Ages. The largest covers 14 acres—more ground than the Great Pyramid of Cheops. But don’t expect the works of the pharaohs: Symmetrical, grass-covered hills sitting in flat, lightly wooded bottomlands are what you’ll find here. The view of the Gateway Arch in distant St. Louis from the 100-foot top of Monks Mound lends an odd sense of grandeur to the site. A sophisticated Interpretive Center (618/346-5160, daily, $7) is a recommended first stop for its exhibits, award-winning multimedia orientation show, and guided and self-guided tours.

The Cahokia Mounds sit in the middle of the American Bottom, a broad floodplain whose gunpowder-black alluvial soils have long been considered among the richest and most productive in the world. However, Charles Dickens was not impressed; after enduring its mud, he wrote in American Notes that the region was an “ill-favored black hollow” which had “no variety but in depth.”

The nearest town to the Cahokia Mounds is Collinsville, a pleasant little place that’s nearly world-famous for its 170-foot-high World’s Largest Catsup Bottle, which rises high above Hwy-159 a half mile south of Main Street, on the grounds of what used to be the Brooks Catsup Company (800 S. Morrison Ave.). This decorated water tower was constructed in 1949 and restored by the people of Collinsville in 1993; it has since been adopted by Collinsville as a supersize symbol of local pride and perseverance.