1. I think you'd better go to your bus station first to find out the situation and see if there is a direct bus to Yishui. If there is, you can take that train directly. Then you can go to the Grand Canyon via Highway 3.
If you don't go to Yishui, take a long-distance bus to Linyi first. Go to the bus station, and then buy a ticket to Yishui. The fare is 20 yuan. It will take more than 2 hours on the way. When you get to Yishui, you can go to the Grand Canyon according to the method of 3.
3. After arriving at Yishui Bus Station, take a taxi directly to the Underground Grand Canyon (Note: it is recommended not to take the bus. I didn't find that there were many cars going to the Grand Canyon, and the car condition was not very good, and the fare was not much less than that of taking a taxi. 12 yuan took a taxi to the Grand Canyon. It may be said, but it is not very expensive, because the starting price of taxis in Yishui is 2 yuan. )
Besides the Grand Canyon, there is an underground gallery, both of which are good. This place is a bit remote. You should take a taxi from the Underground Grand Canyon to 30 yuan, and you should be able to bargain. Go to the gallery and go back to Yishui, you can get it at 35, as long as you can say, bargain, and then it may be difficult.
I didn't go to places like Rainbow Valley and Fluorescent Lake. I hear it's not interesting.
In addition, according to your itinerary, stop in Linyi or Yishui for one day. I suggest you stay in Yishui, which is cheaper. It's good to have a hotel. Keep leaving a message if you want to know. I'll introduce you to some hotels I've seen for your reference!
I hope you have a wonderful trip!