Sometimes it helps to do some research. Spiral showers aren't really based on a spiral, usually. Here's a typical plan for one:
As you can see, the "spiral" is really composed of two half circles; with a 3rd half circle thrown in for good measure. So, you could enable the add-on to draw spirals and fiddle with the settings until you got one that gave what you wanted, or you could model it as two half circles:
The trick here is that the lower half circle's radius is 1/2 that of the upper half circle, and it has been moved exactly that distance to the right.
When the two half circles are overlapped, select all of the vertices and type M and select by distance to merge the two vertices that overlap.
Extrude the resulting curve in the Z distance to the height of the wall.
Add a solidify modifier, and set the width to the wall thickness.
You can extrude the far left vertex to create the side wall, but if you do, do that before you extrude and solidify. Set it to smooth shading and enable Auto Smooth and the result might look something like this:
You can set smooth shading by right clicking on the wall in object mode and selecting Shade Smooth. This will look bad until you enable Auto Smooth by going to the properties editor → Object Data Properties tab → Normals panel and clicking the little box:
You can add the Solidify modifier by going to the Properties Editor → Modifiers Panel; clicking the Add Modifiers box and selecting Solidify:
Enter the wall thickness you want in the Thickness input of the solidify modifier. I used .1m for a nice thick wall: