A few more ideas
National Geographic™ Flower Wood Garden Chews Small Animal | Toys & Habitat Accessories | PetSmart
Natural kabob - can hide treats between the parts
National Geographic™ Nibble Kabob Small Animal Toy | Toys & Habitat Accessories | PetSmart
Tree trunk hideout
KAYTEE
Willow sticks
All Living Things
It's a balance between something that looks nice and natural and something that is good for the hamster in terms of lots of substrate for tunneling, lots of hidey places so not too much open space above them and challenges like getting treats out of toys and finding hidden treats etc.
Something like a cardboard box house, part buried,with a tube leading to it can made a good hide - especially if you cut the bottom out and keep the lid as a lift off roof.