A 20mm thick, large porcelain tile always looks great in the garden. Do you have some photos or an approximate plan of the concrete area and the garden? It would be good to understand where the water would drain and what kind of design could be suggested to make the space look nice.

I think hexagonal tiles will stuck around for another few years - I'd probably give them ten years if I was installing them now. I think it will be the colour and material which will dictate how fashionable they remain. I do like them! They are interesting. Marble will stand the test of time if you buy good quality tiles. If you are buying faux marble then make sure it is top quality too as faux/ersatz products can age badly. Also consider encaustic-style cement tiles (actual ones, not replicas - they feel nicer!) as they are very on trend right now and really suit Victorian houses. Colour-wise is entirely up to you. Neutrals - greys & whites specifically (be careful with cream/beige, right now it can look dated) - are good for bathrooms and if you want to play safe. If you like colour you can go wild with the tiles or add colour to a neutral tile scheme with paint, accessories, towels, paint etc. If your bathroom is small and you plan to stay for a few years then I recommend spending a good part of your bathroom budget on tiles and a good tiler to do them justice. Moreover, unless you are flipping the property, screw the trends and just go with what you like!

Depend on your water quality if it generate mildew often then avoid glass If you use tile avoid bright color grout cause it Will get yellowish or black after sometimes, bigger tile are better because less grout lines to clean Theres Wood called hinoki used in many Japanese onsen, it ressistant to rot, water, insect and has natural antibacterial property plus if in contact with hot water or steam it gives of therapeutic Woody smell https://share.google/Odjcre9a9hXgCmFPO

I can’t see what colour floor & bathroom suite you’ve got, can we have a bigger picture? Tile wise, I’d take the advice of our fab garden design lady who said if we couldn’t match the inside tiles exactly to the outside ones, not to try and have a shade close to them, but instead choose something completely different ;)