Low temperature infrared absorption in the region of intra-shell 4f-4f transitions of Ce3+ ions in bulk yttrium gallium garnet crystals reveals existence of different Ce3+ centers. In addition to the major center, related to Ce substituting yttrium, at least two other centers exist, most probably attributed to the rare-earth antisites, i.e. rare-earth ions at the Ga crystallographic positions. Temperature dependence of the visible absorption related to the 4f-5d transitions shows influence of thermal population of the second higher-lying level of the 2F5/2 ground state, located 159 cm-1 above the lowest level. 5d→4f luminescence of Ce3+ is observed at elevated pressure and shows signatures of pressure-induced crossing of the lowest 5d state of Ce3+ with the conduction band states.