Originally opening in 1973, the SEA Underground is one of the oldest airport people mover systems in the world.

The opening was delayed due to a dispute between the Port of Seattle and Westinghouse, the manufacturer of the system, over contracted costs.

[9] In 1999, the Port of Seattle authorized $142 million to completely overhaul the entire SEA Underground system.

When track maintenance is required on the Green and Blue Lines, the work is typically done overnight, and a single train operates in a shuttle mode.

The main terminal's south station features a series of 56-plus flowers cast of aluminum and aluminum/resin mix created by Nancy Blum.

[15] In the main terminal's north station is a series of nine paintings created by Karen Ganz representing various travelers.