Public spaces, and gardens more specifically, are becoming popular and trendy in Madrid. Most of the outskirt neighborhoods have their own public gardens which are shared by community members and locals.
If you ever visit Malasaña, I would suggest not to miss one of the longest-standing public spaces in town: Patio Maravillas and its partner in crime, Solar okupado Grilo.
It is one of my favorite spots because of all the history that this area has, being the place in which the present Podemos (political party) leaders used to visit while protesting. Many activities are also provided to visitors for free, including but not limited to family friendly events or gardening workshops which will boost your skills like they did mine!
The red Sundays are marked with a highlighter in the calendar as it is an incredible opportunity to meet other people with interests similar to yours. I was lucky I found someone like Melissa there!