MADRID (AP) — The cause of Spain and Portugal’s widespread blackouts remained a mystery on Tuesday, with some isolated disruption remaining after power was largely restored to both countries.

Life in Spain and Portugal began to return to normal Tuesday, a day after a massive power outage paralyzed the Iberian Peninsula, leaving governments, companies and experts scrambling to figure out what went wrong.

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.