I will explain a construction of compact 8-manifolds with holonomy Spin(7) from pairs of asymptotically cylindrical Spin(7) manifolds with compatible cross-sections `at infinity'. The cross-sections are $G_2$ manifolds which may, but need not in general have full holonomy $G_2$. I will discuss examples of the construction, including topologically new examples, and a relation to compact Spin(7) manifolds previously constructed by Dominic Joyce by a different method.