I will review the fascinating physics of cosmological domain walls (DWs). These classical configurations separate different vacua in field theories with spontaneous violation of discrete symmetries. Such theories often appear in high-energy theories beyond the Standard Model of particle physics. I will discuss potential observational problems associated with cosmological DWs and different ways to avoid these problems. Moreover, I will show that DWs are a very promising source of gravitational waves (GWs). In particular, the network of the DWs can be the source of the signal recently observed by NANOGrav collaboration. Furthermore, for different parameter values, one may detect GWs from DWs in currently planned observational missions like the Einstein Telescope, TianQin, Taiji and LISA. This talk is based on e-Print: 2504.07902, e-Print: 2410.21971, e-Print: 2406.17053, e-Print: 2307.04582, e-Print: 2112.12608 and e-Print: 2104.13722.
