On a warm afternoon in June 1889, a pot of boiling glue spilled over in a carpenter’s shop in downtown Seattle. The fire quickly spread and destroyed 25 blocks in the city center in less than 12 hours.
Instead of simply clearing away the ashes and rubble, city leaders saw a chance to fix two major problems. The city often suffered from mud caused by high tides, and many streets were too steep or difficult to use. Officials passed a law requiring all new buildings to be made of brick or stone. City engineers also began a major rebuilding project that eventually buried the original street level deep underground. Now, 137 years after the Great Seattle Fire, visitors to the Pioneer Square Preservation District can still explore the underground remains of old shops, sidewalks and archways.
These spaces once formed the ground floors of businesses in Washington state's growing timber and trading port.
Rebuilding higher above tidal mud
Before the fire, Seattle's business district stood close to sea level along Puget Sound. During high tides, water often flowed back into wooden sewage pipes and turned unpaved streets into muddy pools. The mud sometimes became so deep that horses and buggies were caught in it. After the destruction on June 6, city engineers developed a plan to raise street levels across the business district by 12 to 22 feet.
This process, called regrading, involved building large concrete walls along property lines and filling the central roads with dirt taken from nearby hills.
While the raised streets were being built, property owners faced an urgent business problem. They did not want to wait years for city crews and machines to finish raising the roads. Instead, merchants rebuilt their stone and brick buildings at the original ground level.
For several years, people walking through Pioneer Square saw a strange city with two levels. Raised streets ran through the middle of the blocks, with concrete walls along their sides. Wooden ladders and raised walkways connected people entering shops at the lower level to the higher roads. Once workers had added and leveled all the fill dirt, they built new sidewalks between the retaining walls and the upper parts of the buildings.
This left the original street level buried below ground, creating a network of underground spaces known as areaways.
Infrastructure below current footpaths
According to historical records published by the Seattle Department of Transportation Areaways Program, the city has more than 100 documented areaways, most of them in the Pioneer Square Preservation District. These hollow spaces beneath today's sidewalks formed when property owners enclosed the gaps between their building fronts and the newly raised street walls.
To bring natural light into the dark passageways below, builders installed sidewalk vault lights.
These lights used small, thick glass pieces called prisms, set directly into concrete sidewalks. Over time, exposure to moisture and air caused many of the clear glass prisms to turn purple. This color change resulted from a chemical reaction involving manganese oxide, which was added during glassmaking in the late 19th century.
Research from the National Trust for Historic Preservation identifies these glass prisms as a special feature of Pioneer Square's architecture. Preservation projects continue to focus on repairing leaking or damaged sidewalk vaults across the district. The underground spaces served many purposes over the years. In the late 19th and early 20th centuries, merchants used them to store goods, deliver coal through chutes and house engine rooms.
In 1907, city health officials closed the underground walkways to the public because of concerns about sanitation and the spread of disease. The spaces remained locked away for decades. Some were used for illegal gambling halls or storage, while others were left untouched.
Modern preservation and public access
In the mid-1960s, local historian Bill Speidel began removing debris from selected underground passages and organizing public walking tours through the forgotten spaces.
His work brought attention to the historic structures and helped start a wider preservation movement. This movement eventually helped save Pioneer Square from major urban renewal plans that could have led to its demolition. In 1970, the Seattle City Council officially named Pioneer Square the city's first historic district.
The designation protected its collection of late 19th-century brick buildings built in the Richardsonian Romanesque style. The neighborhood was later added to the National Register of Historic Places. Today, several tour companies, including Beneath the Streets and Bill Speidel's Underground Tour, take small groups through preserved sections of the buried city. Visitors walk down flights of stairs below today's streets and enter dimly lit passageways lined with original iron shopfronts, wooden signs and arched brick supports. Engineers with the Seattle Department of Transportation continue to check and maintain the structures beneath the streets. Through the city's specialized Areaways Program, inspectors carry out regular structural checks and work with private property owners to strengthen aging retaining walls. These efforts help ensure that modern traffic above ground remains safely supported by Seattle's historic underground foundations.