  The goal of this paper is to study the smallest brightening events observed
in the EUV quiet Sun. We use commissioning data taken by the EUI instrument
onboard the recently launched Solar Orbiter mission. On 2020 May 30, EUI was
situated at 0.556AU from the Sun. Its HRIEUV telescope 17.4nm passband reached
an exceptionally high two-pixel spatial resolution of 400km. The size and
duration of small-scale structures is determined in the HRIEUV data, while
their height is estimated from triangulation with the simultaneous SDO/AIA
data. This is the first stereoscopy of small scale brightenings at high
resolution. We observed small localised brightenings ("campfires") in a quiet
Sun region with lengthscales between 400km and 4000km and durations between 10
and 200s. The smallest and weakest of these HRIEUV brightenings have not been
observed before. Simultaneous HRILYA observations do not show localised
brightening events, but the locations of the HRIEUV events correspond clearly
to the chromospheric network. Comparison with simultaneous AIA images shows
that most events can also be identified in the 17.1nm, 19.3nm, 21.1nm, and
30.4nm passbands of AIA, although they appear weaker and blurred. DEM analysis
indicates coronal temperatures peaking at log(T)~6.1-6.15. We determined the
height of a few campfires, which is between 1000 and 5000km above the
photosphere. We conclude that "campfires" are mostly coronal in nature and are
rooted in the magnetic flux concentrations of the chromospheric network. We
interpret these events as a new extension to the flare/microflare/nanoflare
family. Given their low height, the EUI "campfires" could be a new element of
the fine structure of the transition region/low corona: apexes of small-scale
loops that are internally heated to coronal temperatures.
