One idea is to dedicate an area where you let any weeds grow that naturally grow when there is no grass and no lawn mower. Even if the summer is as dry as the last one, you should see many different weeds and herbs grow there.
Have a look at this list of different herbs that are very healthy for rabbits and even have medical properties.
Some of them don't grow naturally in Europe, but many, like fennel, lemon balm, marigold, mint, parsley, rosemary, sage and thyme are common garden herbs that grow well in european climate.
Others like chickweed, cleavers / bedstraw, coltsfoot, dandelion, goldenrod, milk thistle, nettles and plantain / ribwort are natural occuring weeds that many people spend a lot of time removing from their garden beds.
Leafy greens and green vegetables are also good for your bunnies (scroll down for a long list of suggestions).
There is also a list of toxic plants for rabbits, most of them are also known to be poisonous for humans. It's worth to have a printout of it nearby because you might get the idea of feeding some garden waste like potato peels, rhubarb leaves or tomato leaves to them. There are also some unexpected plants among them that you might overlook when they grow wildly in your garden, like bindweed, fools parsley or poppies.
If there is a meadow nearby, you can go there and plug a few handfulls of whatever grows there. A varied diet of many diverse herbs is the best you can offer your rabbits. The worst diet on the other hand, is a carrot and store-bought iceberg lettuce every single day.
Another part of the question was which plants you could have as decoration that the rabbits won't eat.
I honestly doubt that your rabbits would leave any low, green plant alone. If you want something like tulips or similar flowers in your garden (note that tulips grow from bulbs and are therefore toxic to rabbits), you need to surround them with a wire fence.
A better alternative would be bushes or trees. I know from wild rabbits in Berlin that they love any kind of bushes as shelter and hideout. Keep in mind, that evergreens are also toxic, so better stick to leaf bushes. Personally I would choose a plant that is non-toxic and slow-growing, because in a few years, you might have to dig out most of it if it grew too much. Bamboo (a slow-growing variety) and rosehip seem to be suited bushes. Although many fruits like apples, peas, gooseberry, currant, rasberry and blackberry are not toxic, I wouldn't give rabbits free access to them because the fruits have too many calories.