OMA / Koolhaas's 2004 stacked glass-and-steel public library — radical reorganisation of library typology.
From Wikipedia
The Seattle Central Library is the flagship library of the Seattle Public Library system. The 11-story glass and steel building in the downtown core of Seattle, Washington was opened to the public on May 23, 2004. Rem Koolhaas and Joshua Prince-Ramus of OMA/LMN were the principal architects, and Magnusson Klemencic Associates was the structural engineer with Arup. Arup also provided mechanical, electrical, and plumbing engineering, as well as fire/life safety, security, IT and communications, and audio visual consulting. Hoffman Construction Company of Portland, Oregon, was the general contractor.