The 1983 opening of an underground visitor center in Minneapolis represented a victory over an architectural dilemma. Fort Snelling, the US government's regional administrative center during the second quarter of the nineteenth century, was rebuilt as a living history museum during the 1970s. The next step was to build an orientation and interpretive center that would be spacious enough to serve school groups as well as individual visitors. Constrained by a variety of restrictions and objectives, the Minnesota Historical Society commissioned a conceptual design study for the project. The study group ultimately recommended that the center should be an unobtrusive 'non-building.' Appealing but unobtrusive, useful but unnoticeable--what challenging instructions to hand an architect.

The challenge was magnified by the scope of the building's uses. Certainly, it had to serve the usual functions of a visitor center, with a reception area and information desk, a book store and gift shop, and an auditorium where groups could watch films and live presentations. In addition, the Minnesota Historical Society, the proposed building's owner, wanted to include some administrative office space. Furthermore, the structure would also house an archaeological laboratory where artifacts could be analyzed. Considering these space requirements, the architect was faced with the task of hiding a two-story building.

Hiding the building was, in fact, essential. Visitors to the restored fort were supposed to experience the site as it existed in 1827, so the view should not be cluttered with an extra structure. The restored fort sat on a bluff overlooking the confluence of the Mississippi and Minnesota Rivers. The new visitor center could not interrupt the scenic nature of the bluff, whether viewed from the water, from the landward portion of the bluff, or from the cliff on the opposite side of the river. This restriction was motivated not only by aesthetics but also by state laws controlling riverside development.

So, underground it would be. The Historic Fort Snelling visitor center was recessed a story and a half into the ground, and soil was mounded over it, creating a gentle slope atop the bluff. Twenty years later, it still serves as a subtle portal to the rebuilt fortress, with several unusual features continuing to make the experience comfortable and enjoyable for visitors and employees.

Because the prairie grass-covered building cannot be seen from the adjacent parking lot, a tall, stone pillar marks the walkway to its entrance. The psychological impact of entering an underground building is lessened by having visitors walk down a slightly sloping, paved path to the doorway rather than climbing down stairs or descending in an elevator. On the way down the path, they walk beside a stone wall that becomes taller as they progress, rising to normal building height by the time they reach a conventional glass door. Then they walk horizontally into the building, just as they would enter a surface structure.

Inside the building, a broad hallway serves as a reception area where arriving groups can assemble and organize themselves. Because this concourse can be kept at a temperature between the outdoors and the indoor activity areas, it provides a comfortable transition area for visitors. It can also conserve energy by serving as a buffer zone between significantly different exterior and interior temperatures. Along one side of this corridor lie the building's public areas S the information desk, auditorium, and store. Along the other side is a wall filled with windows shielded by vertical blinds; this portion of the building houses staff offices. Along one section of the concourse, sloped glass panels near the floor allow visitors to watch activities in an archaeological laboratory one story below; these windows also provide light and a feeling of spaciousness to the underground lab.

Compared to visitors who are in the building for relatively short periods of time, workers in the two-story office wing have a greater desire and need for rooms with a view. The upper floor, one level below grade, wraps around three sides of an open-air courtyard. The lower floor, a level below this recessed courtyard, could simply have been decorated and illuminated with artificial lights. A somewhat more pleasant effect would have been achieved with a skylight admitting natural light into the space.

However, David Bennett, the visitor center's architect, opted for a more creative measure, essentially making one courtyard wall into a periscope. A hollow wall, several feet thick, is defined by exterior and interior walls. The enclosed, empty space functions as a dual-purpose chamber: fresh air is drawn in through the chamber to circulate through the building, and angled mirrors in the chamber transmit a view of the courtyard to the deeper rooms. At the top, a downward- and outward-facing mirror runs the length of the enclosure, reflecting an image of the courtyard toward the bottom of the chamber. Another large mirror, facing inward and upward, fills the bottom of the chamber, redirecting the courtyard image horizontally through office windows. The lower mirror is tall enough to extend above the top of the windows so that even a person seated at a desk will not see the upper edge of the reflective surface when looking through the window. This periscope device, which Bennett called a "view plenum," effectively creates a virtual courtyard in a narrow, empty column between subterranean offices and surrounding soil.

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