There's lots of sauna herbs, but birch is still the best.
Kimberly asked on the herblist:
"I'm embarking on building myself a Finnish style sauna, I was wondering if herbs are ever used in the sauna, if so which ones?"
Birch is the traditional one: make a bundle of birch twigs and tie them together, then slap the bundle all over you.
I've used leafed-out twigs of other trees, as well: rowan is nice and soft, oak is gnarly, juniper has a nice scent - but our junipers sting, and will leave you covered in tiny red dots.
And I've used pretty much any other trees which haven't run away when I've done the "let's make lots of different sauna bundles" part of one of my summer courses.
Except for pine and spruce, they bleed too much pitch.
I've made sauna bundles with meadowsweet, anise hyssop, nettles (they sting, unless they're first left in a 100 C sauna for 10 minutes - but a 100 C sauna is of course far too hot), horsetail, lots of mints, fireweed (Epilobium), and a couple others.
The trick with flowering herbs is, don't use them in flower, cos the flowerhead is heavy and will drop off at the first or second slapping. Other than that, use any fragrant one you like.
Except, I'd go slow on roses, cos they have thorns, and I'd really truly avoid mullein, cos that is covered in itchy hairs.
Then there's essential oil products and similar, of which you put a few drops into the water which you throw on the sauna stones - I've seen menthol, eucalyptus, artificial birch and tar. None of them are as good as real live birch twigs.