Catalyzes the cyclization of farnesyl diphosphate (FPP) to 10-epi-cubebol. Is also responsible for the formation of many other sesquiterpenes, mainly cadalanes and cubebanes, including 1,10-di-epi-cubebol and the cadalanes delta-cadinene, T-cadinol and alpha-cadinol. (2E,6E)-farnesyl diphosphate + H2O = 10-epi-cubebol + diphosphate Binds 3 Mg(2+) ions per subunit. Belongs to the terpene synthase family.