The cause of the power outage that severely disrupted life in Spain and Portugal on Monday remains a mystery as service was brought back to the Iberian Peninsula.

Millions were plunged into darkness in Europe on Monday as a massive power outage impacted parts of Spain, France and Portugal, but electricity was largely restored by Tuesday morning. The blackout wreaked havoc on travel across the three countries,

Electricity was back in most of the two countries almost 18 hours after a blackout that shut down much of daily life. The cause of the outage remained unclear.