Abstract: Domain walls are two--dimensional defects associated with the spontaneous breakdown of discrete symmetries. It has long been recognized that the formation of these defects in the early Universe can lead to many observable consequences, including the generation of a strong background of gravitational waves (GWs). In this talk, I will focus on domain walls arising in models with axions and axion-like particles (ALPs), and discuss how their dynamics can be affected by their interaction with the thermal plasma. As a relevant application, I will consider the ALP domain wall interpretation of the recent GW detection at Pulsar Timing Arrays, where the annihilation of the wall network is triggered by the QCD confinement. The talk is mainly based on 2306.17830 and 2210.14246.