I immediately googled this and after wading through pages of off-topic information about hot tubs, resort spas, and bath and body recipes using honey, I eventually found some websites that expanded on the information in Natalia's blog and explained that "spa" means "savior" in Russian.
It seems there are actually three August religious holidays in Russia relating to Jesus, known together as "The Three Saviours." These are "the Honey Spas" on August 14th, "the Apple Spas" on August 19th, and "the Linen Spas" on August 29th.
It's amazing what you can learn by collecting world kigo.
honey spas --
she reads a Russia haiku
while toenails dry