Spain and Portugal are racing the setting sun as they respond to a massive, unexplained power outage that knocked out traffic lights, caused chaos on roads and in airports, and threatened to plunge tens of millions of people into darkness on Monday.

The Spain power outage has caused major airport, train, and subway service disruptions. Here's everything to know if you have a trip planned.

A massive power outage hit Spain and Portugal on Monday, shutting down trains, disrupting air travel and leaving large parts of the countries — including the capital cities of Madrid and Lisbon — in the dark.