[Kyrkogrimr]

My dwarf have all loved cork logs (they love them as tunnels, but also to climb all over and usually there are nooks and crannies to hide treats like sunflower seeds for them to hunt for) and seagrass or willow tunnels too - Zooplus often has them at a pretty good price. Mine have also loved having grapevine wood - especially my most recent member of the family who loves to climb his. Bendy bridges are always good, just check for gaps that they could get feet trapped in (I usually plug these up with substrate) and they're brilliantly versatile: bridges, tunnels, ramps. My dwarfs have all loved their sandbaths, and generally seem to think bigger is better - ikea sells screw top cookie jars that are great for that (it's called FÖRVAR and it's £1.50 at my local ikea - not sure if the price varies elsewhere) or mason/cookie jars work well - tip them on their side and you can give them plenty of sand to play in without it going everywhere.
Whimzees are great - I've only had one hamster who doesn't like them and I think he's just a bit picky to be honest lol All of my other hamsters have loved them, usually store them in their nests, though Palladium is keeping his out in the open, so I've been able to see how quickly he's destroyed it lol
The only thing I would say is that all of my hamsters, especially the dwarfs, like to have their cage quite cluttered with as many hidey holes as possible - too much open space or areas that don't have much coverage from above tends to result in them being nervous/grumpy/less friendly, depending on the individual. Other more experienced members might disagree (and I'll happily accept correction) but my experience has been that more cover and hiding places generally means happier hamster.
One thing I usually find works really well is burying (or partially burying) tunnels - I usually shelter the entrance with a bendy bridge too. I only do this with natural materials personally - I've read about plastic tunnels not being great at the best of times in terms of heat and ventilation, I don't think burying them under substrate would improve that! But I only really use plastic tunnels with Carbon anyway and mainly because he has a love affair with them. He's a rescue and he grew up in a small plastic cage with plastic tunnels, so he enjoys them and definitely seems happier with a few of them in his cage so I include them; one is mostly above the substrate and dips under to give him another entrance under one of the walls of his house, the other is a few of the curved ones joined together with one end leading into the substrate to start a tunnel that he digs himself.
Hope some of that is useful!