Alanna Gladstone, a 40-year-old film editor, had landed in Portugal’s capital, Lisbon, on a flight from New York hours before the outage. She checked into her Airbnb and took a nap; by the time she woke up, the technology that the country takes for granted had gone dark.

Power is almost fully restored in Spain and Portugal a day after a major blackout. But many questions remained about what caused one of Europe’s most severe blackouts. Spanish electricity operator Red Eléctrica said that more than 99% of energy demand had been restored by 7 a.

The Madrid Open will resume play this morning after the tennis tournament was hit by the vast power outage across Spain and Portugal on Monday.