Various cage accessories can be placed in a hamster's cage to provide extra stimulation and a more interesting environment for the hamster.
Information about hamster houses.
Information about hamster exercise wheels.
There are various wooden blocks and climbing frames available for hamsters with holes the hamster can travel through. These are more suitable only for Dwarf Hamsters as the holes on many are too small for a Syrian Hamsters to climb through.
There are various play "boots" designed for hamsters with holes that the hamster can climb in and out of. Be sure to check all holes are a suitable size to allow the hamster to easily climb through as some are only suitable for smaller hamsters.
A sand bath can be provided by placing a suitable sized dish in the cage filled with chinchilla sand. Ceramic or Metal dishes which are not easily tipped are best used. Hamsters, particularly Dwarf Hamsters, appreciate having a dish of sand to roll in and this helps to remove the greasiness from the coat - remember in the wild they live in deserts so this is natural for them.
Many Pet Shops stock mineral blocks and salt blocks for hamsters. These are not really necessary for the hamster's well being.
Old cardboard tubes or toilet roll tubes can be provided for the hamster and it will enjoy using it as something to climb through, on or nest in as well as chewing it to pieces.
Wood gnaws are available in Pet Shops or you can provide your own by supplying the hamster with a piece of apple branch. These provide the hamster with something on which to gnaw in order to keep its teeth trim.