An increasing number of star-forming regions and young star clusters are detected in $\gamma$-rays, which hints at ongoing particle acceleration. These regions harbour young massive stars, whose powerful winds collectively blow superbubbles (SBs) containing large-scale shocks and tenuous, hot, turbulent plasma. Investigating the physics of SBs is necessary to clarify their role as galactic cosmic ray (CR) sources and their ability to reach energies ${>}1\,$PeV. In Härer et al. 2023, we presented a one-zone emission model for the ring-like H.E.S.S. source surrounding Westerlund 1, a prototypical example for a young massive cluster. The spectrum and the morphology of the source are consistent with a leptonic inverse Compton model, in which the acceleration takes place at the cluster wind termination shock. The ring-like morphology, overall size of the emission region, and energetics disfavour both hadronic models and alternative acceleration sites. Our results showcase the impact of certain environmental parameters on key characteristics of the system. For example, the strength and topology of the magnetic field are critical for the maximum energy, as they affect the acceleration time and particle transport. We briefly summarise the key findings of the Westerlund 1 phenomenological analysis, followed by a report on ongoing work on MHD simulations of star cluster wind.