Abstract: I will discuss joint work with Calum Ross where we construct large families of Yang-Mills instantons, i.e. solutions of the anti-self-duality equations of 4-dimensional gauge theory, on gravitational instantons with ALF (asymptotically locally flat) asymptotics. The latter are certain complete non-compact hyperkähler 4-manifolds which are prototypical examples of codimension-1 collapsing behaviour of special holonomy Ricci-flat manifolds. Our construction describes the behaviour of Yang-Mills instantons on ALF spaces in the collapsed limit where these 4-dimensional geometries are close to a 3-dimensional collapsed limit space. In this limit, the instantons are well approximated by superpositions of simple localised building blocks constructed out of monopoles on R^3.