A friend sent us this link today, suggesting it might be good for a few days in the mountains.
I can’t read a word of Chinese, but with help from Google Translate, I eventually found that it is the Hoshinoya Resort at Guguan - to the east of Taichung on the highway to Taroko. The rates are a “bit eyewatering” though, and even looks to be booked out for a while.
Great bargains in Taipei hotels right now. We stayed at the Banqiao Hilton last night in their executive suites for 6k (3 people). All you can eat and drink from 5.30 to 7.30. Standard buffet breakfast.
The Regent is offering a package of 2 nights for 6k.
Bring sacks of money. 
Btw, Commonwealth Magazine published a nice piece on this property, asking if the domestic tourism industry in Taiwan is ready to up its game and deliver a higher-market experience:
Guy
can you see the turtles if you’re only snorkeling?
otherwise, what’s the easy way to see them up close?
If you want to see the turtles, the place to go is Xiaoliuqiu, not Green Island, as far as I have heard.
Guy
Xiaoliuqiu is the place to go in Taiwan if you want to snorkel with turtles.
Edit: Oops, @afterspivak got in there just before me.
I’m not sure but I’m guessing no unless you know exactly where to look and you are a decent free diver. I remember we were quite deep when we saw the turtles. Over 10m maybe. I can’t remember.
Saxon version linked below.
Their bassist rocked
Best in the world