We present El Bongosero, a large-scale, open-source symbolic dataset comprising expressive, improvised drum performances crowd-sourced from a pool of individuals with varying levels of musical expertise. Originating from an interactive installation hosted at Centre de Cultura Contemporània de Barcelona, our dataset consists of 6,035 unique tapped sequences performed by 3,184 participants. To our knowledge, this is the only symbolic dataset of its size and type that includes expressive timing and dynamics information as well as each participant's level of expertise. These unique characteristics could prove to be valuable to future research, particularly in the areas of music generation and music education. Preliminary analysis, including a step-wise Jaccard similarity analysis on a subset of the data, demonstrate that this dataset is a diverse, non-random, and musically meaningful collection. To facilitate prompt exploration and understanding of the data, we have also prepared a dedicated website and an open-source API in order to interact with the data.