A singular symplectic variety of dimension 6 with a Lagrangian Prymian fibration

Abstract: A projective symplectic variety $\mathcal{P}$ of dimension 6, with only finite quotient singularities, $\pi(\mathcal{P})=0$ and $h^{{(2,0)}(\mathcal{P}_{smooth})=1$,} is described as a relative compactified Prym variety of a family of genus 4 curves with involution. It is a Lagrangian fibration associated to a K3 surface double cover of a generic cubic surface. It has no symplectic desingularization.