The Real Jardín Botánico Alfonso XIII, located at the University Complutense of Madrid, is a beautiful botanical garden where you can explore nature and mathematics through stunning outdoor exhibitions. While entry is free, make sure to check their opening hours as they vary depending on the day. Unfortunately, guided tours are currently suspended, but you can still enjoy the garden on your own or with a small group. Don't miss out on this green oasis in the heart of Madrid!