Martello Alley is Ontario's only open-air art gallery and is considered one of the best hidden gems in the province. The company, a subsidiary of TripAdvisor, analyzed data from over 1,000 local destinations to compile its ranking of the world's best hidden gems. Twenty-six reviews called the Martello Alley a hidden gem, which represented 6.7 per cent of reviewers holding that opinion of the destination. Martello Alley wasn't always a hidden gem. Martello Alley is open daily from 10:00 a.m. to 5:00 p.m., all year round.