These were our Syrians favourite toys
Rat sputnik and hyacinth tunnel (the small size tunnel is plenty big enough even for a large Syrian). It has holes in the side to go in and out of and is chewable as well.
Rat rations let you choose the top and bottom colours of the rat sputnik.
Sputnik - XL - £4.99 : ratRations.com
This is what they look like hanging in a cage. They work best next to a shelf so they can get access to it easily
https://www.google.co.uk/search?q=ra...CRBksQ_AUIBigB
Hyacinth tunnel small
https://www.amazon.co.uk/d/Small-Ani...yacinth+tunnel
Other than that, generally hidey places, a good sized house to build a big nest in, lots and lots of substrate and a shelf or level - plus chews.