This manuscript is the first scientific publication of the project “BioBlitz Azores". The project was launched in 2019 and had a second event in 2023 under the scope of the FCT-MACRISK project, surveying the historic public garden "Jardim Duque da Terceira", in the historical centre of Angra do Heroísmo, Terceira Island (Azores, Portugal). In addition to contributing directly to the knowledge of Azorean biota, BioBlitz Azores aims to engage the non-scientific community - including volunteers, amateur naturalists, students, teachers, families and other garden visitors - to foster a sense of community and raise awareness about Azorean biodiversity and its conservation. Under the scope of two BioBlitz events, the list of taxa of the historic garden of "Jardim Duque da Terceira" (Terceira, Azores, Portugal) was updated and presently includes 72 lichen species, 55 vascular plant species, 96 arthropod species, 14 bird species and three freshwater vertebrate species. In the realm of lichens, two species are new records for Portugal and Macaronesia, one species is a new record for the Azores and nine species are new records for Terceira Island. This is the first academic publication for 11 of the 12 lichen species. The survey of arthropods yielded an inventory encompassing a total of 96 taxa, with 78 of these identified to the species or subspecies level; amongst the identified taxa, three are endemic, 32 are native, but not endemic, one is of indeterminate origin and 42 are introduced. Notably, a single specimen of the rare endemic spider, Savigniorrhipis acoreensis Wunderlich, 1992 was observed for the first time at this low elevation (garden elevation: 29-60 m a.s.l.). The species is typically found in the canopies of endemic trees species in native forests at mid- to high elevations (500-1000 m a.s.l.) and its presence in the garden suggests a source-sink dynamic of this extremely dispersive species between native and anthropogenic habitats. Regarding vascular plants, 54 taxa were recorded in the garden, comprising one endemic, one native, three with indeterminate origin and 49 introduced ornamental species. Amongst birds, 14 taxa were registered, including seven Azorean endemic subspecies, two native species and four introduced taxa. Three freshwater vertebrate species were recorded during the survey, all of which are exotic species that have been introduced to the garden.