The original memorial, completed in 2007, was unlike any monument in Spain. An eleven-meter-tall glass cylinder rose above the station, composed of glass blocks on a raised platform. Inside, a transparent membrane was inflated by air pressure, rising balloon-like within the cylinder. Printed on that membrane were hundreds of messages of grief, sent from all over the world in the days following the attack. Below, an empty room was bathed in blue light that filtered down through the glass structure alone. At night, lamps at the cylinder's base illuminated it from within, making it visible throughout the neighborhood, a quiet glow above a station that never stops moving.

King Juan Carlos, Queen Sofia, and Prime Minister Jose Luis Rodriguez Zapatero attended a ceremony at the memorial on March 11, 2007, the third anniversary of the bombings. Wreaths were laid at the base of the tower. Mourners observed three minutes of silence. The memorial became a place of annual pilgrimage, a fixed point of remembrance in a city that had no choice but to keep moving through the very station where the horror occurred. Three weeks after the bombings, on April 3, several of the suspects blew themselves up during a police raid on their apartment in Leganés, killing a special forces officer. The memorial honored him as well.

In 2023, the city began dismantling the glass memorial to make way for the expansion of Madrid Metro Line 11. The decision was practical and painful. By February 2024, the cylinder was gone. Ahead of the twentieth anniversary on March 11, 2024, a temporary beam of cobalt blue light was projected skyward from the site, a spectral echo of the structure that had stood there. On March 10, 2024, a new underground memorial was inaugurated beneath the original location, its cobalt blue walls chosen by the victims' associations. Engraved into those walls are the names of the 193 people who died and some of the messages that had once floated inside the glass cylinder above.

The color cobalt blue runs through both versions of the memorial like a thread connecting past to present. The original interior glowed blue from filtered light; the new underground space is defined by blue walls. It is a deliberate choice by the families, a color that feels both solemn and infinite, neither warm nor cold. Visitors descend into the new memorial through the Atocha Metro vestibule, passing from the noise of a functioning transit hub into a quiet space where names and messages cover the walls. Floral tributes and candles appear regularly, left by people who remember what happened here, or who simply feel the weight of a place where ordinary mornings were shattered.