[emma_mcraf]

I would say no to the bark as it’s hard for them to walk on and isn’t great for their legs. Also it can stick into them, I’ve read of tortoises ingesting it and they harbour mound spores if damp.
Slate is okay providing it won’t get too hot. You really don’t want it getting heated too much by the sun as it’ll burn your torts.

I added extra interest to the substrate outside with pebbles, little sterilised logs, pots, plants, shelters, etc. I’ve used large limestone chippings and I know some people use pea gravel.
It’s fun to plant up areas and add extras. Hope Darla and Dory enjoy their new areas. Bear in mind they don’t always like too much change at once, but I’ve always found mine have been curious to investigate anything new.