Hotel Savoy in Opatija now has an indoor swimming pool on the lower floor facing the sea.
There is also now a sauna, and massage and other spa services available. This is not mentioned in the 2019 Rick Steves Europe Croatia and Slovenia book.
I am in Opatija now and just spent all morning by the indoor pool. As it’s still early (end of May), and the weather is a bit iffy outdoors, the outdoor pool at Hotel Savoy is not yet functional.
So it was a real surprise to find a beautiful indoor pool!