A detection of primordial gravitational waves in the next future would imply that the inflaton traversed distances in field space larger than the Planck scale. Axions are ideal candidates to realize such transplanckian displacements because of their defining shift symmetry. The addition of a small polynomial potential is known as Axion Monodromy and provides a promising framework for Large Field Inflation. The aim of this talk is to discuss two complementary aspects of this construction. Firstly, we investigate constraints on the field range from general expectations about the properties of Quantum Gravity. In particular, we focus on the implications of the Weak Gravity Conjecture (WGC) and present a bound on the inflationary field range. Secondly, we explore the post-inflationary phenomenology of the model. We show that the potential can exhibit local minima after inflation. In certain regions of parameter space the inflaton can then populate more than one of these vacua. This corresponds to a phase decomposition, followed by the collision of cosmological bubbles and by the production of gravitational waves.