I will discuss an instanton solution preserving AdS boundary conditions. It arises in a compactification of M-theory to four dimensions, keeping a single scalar coupled to gravity with a phi to the 4th potential. We study the holography of this solution in the context of a toy model, where the effective boundary CFT is a conformally coupled scalar with a phi to the 6th potential in three dimensions. We match bulk and boundary instanton solutions as well as fluctuations around them. Using a form of radial quantization we show that quantum states in the bulk correspond to multiply-occupied single particle states in the boundary theory. I will discuss the interpretation of the instanton in the dual CFT as a deformation by a triple-trace operator, and how the instanton signals an instability of the theory under this deformation.