Robert Chambers Reamer (1873–1938) was an American architect, most noted for the Old Faithful Inn in Yellowstone National Park.

The firm produced a wide variety of projects, but the only surviving example of Zimmer & Reamer's work is the George H. Hill Block in the Gaslamp District.

The Old Faithful Inn was commissioned in 1902 by Child, and funded with loans from the Northern Pacific Railway, using laborers who were experienced railroad trestle builders.

The depot opened first, in 1903, and embodied many design features that Reamer explored on a grander scale at the Old Faithful Inn.

The Old Faithful Inn is a National Historic Landmark, honored as the inspiration for a rustic style of architecture popular throughout the western United States.

The rustic style is sometimes considered a branch of the Arts and Crafts movement, which emphasized fine, hand-hewn details and harmony with the surrounding environment.

Inside, a spectacular, six-story lobby features native lodgepole pine balconies, and it is anchored by a 500-ton rhyolite chimney and fireplace.

At the same time that Reamer was building the Old Faithful Inn from the ground up, he was also overseeing the expansion of the Lake Yellowstone Hotel.

In complete contrast to the Old Faithful Inn, the Lake Yellowstone Hotel was originally an austere clapboarded barn-like structure.

After the major work of 1903, Reamer spent ensuing years designing and supervising a variety of supporting buildings and residences around Yellowstone, particularly in Mammoth Hot Springs and Gardiner.

[8] The design bore a close resemblance to Frank Lloyd Wright's Prairie style work, with a strong horizontal emphasis and a commanding roofline.