City Nature Challenge Madrid 2018

The City Nature Challenge Madrid 2018 (Biomaratón, in Spanish) is an event where citizens from the metropolitan area of Madrid will upload as much biodiversity observations as possible to Natusfera (natusfera.gbif.es) in order to be the winner city of the international competition City Nature Challenge (organized worldwide by the California Academy of Sciences and the Natural History Museum of Los Angeles County).
Useful information: 
There are many activities / bioblitz organized by several local entities, not just by the Royal Botanic Garden. Check all activities scheduled at: http://www.gbif.es/proyecto/biomaraton-madrid-2018/ (in Spanish). Most of the activities are free but you need to register.