Once a royal hunting ground, Madrid's 300-acre Retiro park is now a gathering place for commoners of every stripe, who come to enjoy its forests and ponds, playgrounds, and paths. If you tire of its 15,000 trees, formal gardens, or exhibitions, try taking a boat ride on the big central lake or attending a puppet show. There is also the Crystal Palace, built to house a collection of exotic plants from the Philippines, and an observatory for stargazers. On weekends, look out for street musicians, jugglers, clowns, and even gypsy fortune-tellers.
Hours vary by season.