Good toys are natural toys!Avoid plastic at all costs,it isn't breathable at all so it will get smelly and could cause breathing problems for any rodent.Plus,if it gets chewed it is extremely unsafe,so anything plastic should be exclusively for playpen time or something like that
Something like a hay tunnel or wicker tunnel would be really good actually,since it would be a chewable tunnel that is breathable and natural and completely safe.Just make sure you get ones that are actually natural and not the snak shack style houses,as those are very bad and aren't particularly healthy for any animal to be ingesting due to chemicals added and unhealthy ingredients as well as pine shavings being used in them which can cause allergic reactions.
JR Farm Heu-Tunnel günstig bei zooplus This would be good,since it is just a hay and parsley tunnel with safe ingredients.
Korkröhre günstig bei zooplus Cork rounds and cork in general make lovely additions to cages,and these would make excellent tunnels but once again unlike plastic tubes these are completely safe!
Weidenbrücke für Nager günstig bei zooplus This is just one of many bendable bridges you can purchase!Bendable bridges are great since they can perform several tasks at once in the habitat,such as being a ramp as well as a hiding place.
Eck-Spielhaus günstig bei zooplus This is just a wonderful natural wooden corner house!It's always good to be able to offer multiple hiding places,but a labyrinth style house would be better than having open houses.However,it is still good to at least offer a variety of hiding places instead of only giving one or two of the same type.
Grashaus XL günstig bei zooplus This hay house is an example of several similar ones.It's not the greatest price though,especially if you're worried about it lasting for a good amount of time relative to the price point.
http://www.zooplus.de/shop/nager_kle...ubehoer/160840 Another hay house,but a much better size and price
There are tons and tons of options out there,but there are also lots of DIY projects which would be just as good such as a simple cardboard box labyrinth house