  Strong lensing offers a precious opportunity for studying the formation and
early evolution of super star clusters that are rare in our cosmic backyard.
The Sunburst Arc, a lensed Cosmic Noon galaxy, hosts a young super star cluster
with escaping Lyman continuum radiation. Analyzing archival HST images and
emission line data from VLT/MUSE and X-shooter, we construct a physical model
for the cluster and its surrounding photoionized nebula. We confirm that the
cluster is $\lesssim4\,$Myr old, is extremely massive $M_\star \sim
10^7\,M_\odot$ and yet has a central component as compact as several parsecs,
and we find a gas-phase metallicity $Z=(0.22\pm0.03)\,Z_\odot$. The cluster is
surrounded by $\gtrsim 10^5\,M_\odot$ of dense clouds that have been
pressurized to $P\sim 10^9\,{\rm K}\,{\rm cm}^{-3}$ by perhaps stellar
radiation at within ten parsecs. These should have large neutral columns
$N_{\rm HI} > 10^{22.5}\,{\rm cm}^{-2}$ to survive rapid ejection by radiation
pressure. The clouds are likely dusty as they show gas-phase depletion of
silicon, and may be conducive to secondary star formation if $N_{\rm HI} >
10^{24}\,{\rm cm}^{-2}$ or if they sink further toward the cluster center.
Detecting strong ${\rm N III]}\lambda\lambda$1750,1752, we infer heavy nitrogen
enrichment $\log({\rm N/O})=-0.21^{+0.10}_{-0.11}$. This requires efficiently
retaining $\gtrsim 500\,M_\odot$ of nitrogen in the high-pressure clouds from
massive stars heavier than $60\,M_\odot$ up to 4 Myr. We suggest a physical
origin of the high-pressure clouds from partial or complete condensation of
slow massive star ejecta, which may have important implication for the puzzle
of multiple stellar populations in globular clusters.
