That really depends on the chapter. But if you click here, you can find more comprehensive information regarding this building.
EDIT: I needed to do a double-take here. What I had was "Burning Pool" in my city and noticed that I too had a Somnial Pool in my inventory. Only one. Where'd I get it from?
I suspect the season thing, but I didn't pay attention to my prizes. Just blind clicking to get goodies before they went away. Either way, from a chapter 13 perspective, it trades off a fair bit of its already low culture for a slightly higher mana generation. They've also got the same footprint as each other (and Festival Merchant, which I've kept as a holdover from my chapter 9 and 10 days because... mana)
EDIT2: Holy heck, some of that text above was bad info. I need a side-by-side rather than a pageflip.
EDIT3: A side-by-side. Somnial is just better in every way [EDIT4: In comparison to each other. Festival Merchant, which can be crafted in MA, is functionally identical to the inferior Burning Pool up to the halflings chapter and beyond, where FM makes seeds instead. Otherwise, its production is identical. Its culture values are identical. The space taken is identical.]
View attachment 15397View attachment 15399
EDIT5: Yeah. I'm putting this in my city ASAP