The practical risks are the ordinary big-city ones: pickpocketing on crowded Metro cars and in the atrium, and overcharging by unofficial taxis. Travel by Metro Line 6 or Line 3 in daylight, or use a ride-hail app or hotel taxi; keep the passport in the hotel safe and carry a copy. Stay within the sanctuary and the main avenues after dark.
Solo visitors who prefer company can join the basilica's guided visit (Monday to Saturday, 11:00 a.m. and 3:00 p.m., reservation required) or hire a licensed guide. Avoid December 11 to 12, when crowds of millions make movement difficult. Check the advisory before departure, since levels change.