Convert basement into wellness oasis – Assessment

I would like to have a room of about 25 square meters in the basement converted into a wellness area. I myself have no knowledge about construction/renovation, do not know anyone who is familiar with such things, and therefore cannot estimate whether/how this would be possible.

Step 1 would now be to first gather assessments/opinions on whether this is realistically possible, what would need to be done, and what financial expenses I would face (so only the scale of costs, not concrete amounts).

The room currently

This is not a typical cold/damp basement room but was used for a long time as a bedroom and office.
One door, a double casement window, a few power outlets, a chimney flap, a radiator, tiled floor.
No water/wastewater, no high-voltage power, no ventilation.

What I would like

[*]a small sauna (for 2 people)
[*]a shower, possibly with an integrated steam bath (otherwise maybe a separate steam bath, or none at all)
[*]something like a fountain (fixed to the floor) – the sound of trickling water relaxes me enormously; ideal if you can sit on the edge or put your feet up
[*]a ventilation system (exhaust system?) – partly of course to prevent mold, but also because the sound of ventilation relaxes me (as long as it is a steady noise)
[*]indirect lighting under the ceiling, all around the room

What is important to me: everything should appear seamless, that is, the design well coordinated, almost like the wellness area of a small hotel. Therefore, I estimate I would need an expert here who offers everything from a single source or coordinates it completely and takes care of the details (for example, that cables are well concealed; that the sauna does not look "placed on" but is connected to the floor and tiles; etc.).

My questions

[*]Are there experts who offer something like this from a single source (or coordinate it completely)? What should I be looking for?
[*]Is it feasible to equip a room afterward with water and wastewater connections? The main water connection is also in the basement. I can somehow imagine that you "simply" connect another line to the existing pipe and lead it to the room. But how does that work with the wastewater? Does the floor need to be broken up and hollowed out?
[*]If high-voltage power is required for the sauna – is it easy/well feasible to retrofit?
[*]The floor is tiled (however, I would like to have different tiles), but the walls and ceiling are unplastered. Do the walls/ceiling need to be specially treated so that no moisture problems occur?
[*]Is it enough for the room size (about 25 m²) to have one unit installed on/in(?) the wall, or is something needed that sits in multiple places under the ceiling?
[*]What am I not thinking of?
[*]Am I crazy?
[*]How do you estimate the costs? (also happy about estimates for individual parts, if you are familiar with them)

Are there experts who offer something like this from a single source (or coordinate it completely)? What should I be searching for?

Look for high-end bathroom designers. Or sauna builders.

Is it doable to retrofit a room with water and wastewater connections afterwards? The main water connection is also in the basement. I can somehow imagine that you can "simply" connect another line to the existing pipe and lead it to the room. But how does the wastewater work? Does the floor have to be broken up and hollowed out?

It depends on the exact situation. Lifting station/sump (with pump) are some keywords here.

If the sauna requires three-phase power – is that easy to retrofit?

That depends again. Three-phase power = 400V is suitable for many good (more powerful) sauna heaters. Where is the fuse box? How can cables be laid?

The floor is tiled (although I would like different tiles), but the walls and ceiling are unplastered. Does one have to treat the walls/ceiling in a special way so that there are no problems with moisture?

Wellness oasis and then bare walls? That won’t work at all. Good ventilation is the magic word. Regardless of tiles, plaster, wood paneling, or whatever. Basement insulated from the outside? Otherwise, humidity will simply condense on the cold basement walls.

For the room size (about 25 m²), is one unit installed on/in the wall enough, or do you need something that is installed in several places under the ceiling?

What is "one unit"?

Am I crazy?

Great idea!!! Who wouldn’t want something like that. Even if the sauna at home consumes a lot of electricity and with the investment you could spend your evenings twice a week in a great sauna facility for the rest of your life.

How do you estimate the costs? (gladly just for individual parts if you are familiar with them)

No idea. For high-quality equipment – you want it to look nice after all – I would guess around €30K (+/- €10K).

Jo sounds all doable. I can agree with my predecessor. I think costs will be around 30 to 50,000 euros.

Are there experts who offer something like this from a single source (or coordinate it completely)?

For money, you can get anything. How much do you want to invest? Numbers for orientation have already been mentioned.

The budget is one thing. I hardly know any wellness area in the basement that is actually used. Something like that makes more sense on the garden level, sleeping level, or bathroom area. You need 400V, water, sewage... With 30k-50k you can certainly do something. There is no upper limit. However, you need wall breakouts and also have to tear up the floor. Since I am not a sauna-goer, I would rather build a small pool in the garden.