Robert Mills House, Historic house museum in Columbia, United States.

The Robert Mills House is a two-story brick building with four Ionic columns in Columbia, South Carolina, occupying a full city block on Blanding Street. The main facade features round-arch windows, and the building is topped by a gabled roof.

Built in 1823 to a design by Robert Mills, the house was commissioned by Ainsley Hall, who died before it was finished. It later served for many years as part of the Columbia Theological Seminary campus until the seminary left Columbia in 1960. Threatened with development, it was acquired by Historic Columbia and restored, opening as a museum in 1967.

The house is also called the Ainsley Hall House, after the man for whom Robert Mills designed it in 1823; Hall died before it was finished. Its rooms are furnished with early 19th-century decorative arts, including American Federal, English Regency and French Empire pieces, so visitors can compare three national styles side by side.

Guided tours are the main way to visit the interior, so it is worth checking opening times before you go. The house sits in a quiet part of Columbia, making it easy to walk around the grounds at your own pace.

The entrance hall has a hidden stairway behind a door that mirrors a false door on the opposite wall, creating a symmetry that most visitors do not notice at first. Looking carefully at both walls at the same time is the easiest way to spot the trick.