During a week, from September 4th till September 10th, it is possible to try a mindfulness guided class at Meditación Kadampa. There are two sites, the one situated at Malasaña and other at Majadahonda, and both offer one week of open classes.
It is not necessary to book and you can repeat al the classes that you want for free until capacity is reached. You will improve your concentration, the quality of your ideas and stay positive. The structure of the class is a guided meditation at the beginning of the class, a explanation step-by-step about mindfulness and a final guided meditation. Each class is 60 or 90 minutes long.
Here are the timetables and if you want more info, consult their website: