Electricity is pulsing through Spain and Portugal again after a massive outage knocked out power in both countries on Monday. So too are questions.

Millions were plunged into darkness in Europe on Monday as a massive power outage impacted parts of Spain, France and Portugal. The blackout wreaked havoc on travel across the three countries, and the impacts extended beyond there, too.

Play was halted at the Madrid Open tennis tournament, while the Spanish capital's metro system ground to a stop.