String theory generically predicts a landscape of axions. However, most studies of axion defects focus on a single-field setup. In this talk, I will discuss the nontrivial dynamics that emerge in a two-axion framework. Due to the mixing of the two axions in the potential, cosmic strings and domain walls exhibit a variety of phenomena specific to multi-axion systems. For example, strings of different axions can form “string bundles”, domain walls of one axion can induce domain walls of another, and potential bias can temporarily arise. I will also discuss the cosmological implications such as dark matter production and gravitational wave emission.