With 22 million residents, Mexico City is home to a bustling economy, stunning colonial architecture and delicious cuisine. But there are some interesting facts about this massive metropolis that you might not be aware of.

For starters, it’s the most populous metropolitan area in the world. It also happens to be at the highest altitude of any major city in Latin America. That’s a fact that might explain why chilangos and capitalinos often experience symptoms of altitude sickness.

The city is situated at an altitude of 7,349 feet. That’s significantly higher than the 5,280-foot altitude of Denver. That’s why many visitors to the city will feel altitude sickness symptoms such as nausea, headaches and fatigue.

If you’re traveling from sea level to Mexico City, you may want to spend a few days in the city before heading to higher elevation areas such as forested mountains where Monarch Butterflies gather to overwinter or the forested hills and canyons of Copper Canyon. This will help you acclimate to the lower oxygen levels and avoid altitude sickness symptoms.

Another way to avoid altitude sickness is to stay hydrated and drink lots of water, even if you’re not thirsty. You can also take a non-drowsy antihistamine like Dramamine to prevent symptoms. Or try homeopathic remedies such as chlorophyll drops and wristbands. You can buy them at most pharmacies in the city.