  We use the TNG50 simulation of the IllustrisTNG project to study cold, dense
clouds of gas in the circumgalactic media (CGM) of Milky Way-like galaxies. We
find that their CGM is typically filled with of order one hundred (thousand)
reasonably (marginally) resolved clouds, possible analogs of high-velocity
clouds (HVCs). There is a large variation in cloud abundance from galaxy to
galaxy, and the physical properties of clouds that we explore -- mass, size,
metallicity, pressure, and kinematics -- are also diverse. We quantify the
distributions of cloud properties and cloud-background contrasts, providing
cosmological inputs for idealized simulations. Clouds characteristically have
sub-solar metallicities, diverse shapes, small overdensities ($\chi = n_{\rm
cold} / n_{\rm hot} \lesssim 10$), are mostly inflowing, and have sub-virial
rotation. At TNG50 resolution, resolved clouds have median masses of $\sim
10^6\,\rm{M_\odot}$ and sizes of $\sim 10$ kpc. Larger clouds are well
converged numerically, while the abundance of the smallest clouds increases
with resolution, as expected. In TNG50 MW-like haloes, clouds are slightly
(severely) under-pressurised relative to their surroundings with respect to
total (thermal) pressure, implying that magnetic fields may be important.
Clouds are not distributed uniformly throughout the CGM, but are clustered
around other clouds, often near baryon-rich satellite galaxies. This suggests
that at least some clouds originate from satellites, via direct ram-pressure
stripping or otherwise. Finally, we compare with observations of intermediate
and high velocity clouds from the real Milky Way halo. TNG50 shows a similar
cloud velocity distribution as observations, and predicts a significant
population of currently difficult-to-detect low velocity clouds.
