I did this in the afternoon (after visiting Megijima in the morning). Took the Kotoden and then the bus to Yashima mountain top. Considered walking up but seems a little difficult to find the way. Didn’t regret taking the bus actually, because even the paved road up the mountain was a little steep at times and I was a bit tired from cycling in the morning. For those who want to hike up, google map “Takamatsu Shiritsu Yashima Elementary School, 1205-1 Yashima Nishimachi, Takamatsu-shi, Kagawa-ken 761-0113, Japan” and once you are there you should see signs everywhere pointing towards the start of the hiking route. It’s a residential area with some people roaming around occasionally so you should be able to ask for directions if you need.
At the mountain top, there isn’t actually too much to do apart from taking a few photos at the various viewpoints and a few cherry blossom trees (I went in early April). There is an abandoned hotel-like building that looks like it will collapse anytime, with broken glass doors and you can peek inside and see abandoned old school arcade games - I can just picture it turning itself on at nighttime like in a ghost movie! Kinda interesting to look at.
So one of the main things I wanted to check out based on the reviews below was the abandoned upper cable car station. Took me a while to find and I finally found the location on google map - search for “Japan, 〒761-0111 Kagawa-ken, Takamatsu-shi, Yashima Higashimachi, 屋島城跡展望台” and then continue along the road south (you will see some unnamed buildings on google map). It was indeed the most interesting thing out of Yashima apart from the view, for me at least.
I then walked down Yashima (there are some steps down from one of the temple entrances - just google map for the route down to the elementary school mentioned above and the route should show). The walk down was just under an hour. When I got down, I wanted to check out the obsolete lower ropeway station as well - this is actually on google map known as “Japan, 〒761-0112 Kagawa-ken, Takamatsu-shi, Yashima Nakamachi, 168−5, 屋島登山口駅跡”. Wasn’t as creepy as I thought though maybe because it was still bright! I find the upper ropeway station a little creepier though maybe it was because I kept hearing weird noises in that area (fairly isolated, didn’t bump into any other tourists) and kept thinking a wild boar was about to attack me anytime. There were also a couple of cats staring at me at the creepy upper ropeway station...
All in all, the views were great at Yashima, the abandoned ropeway stations were interesting, and I would’ve loved to stay for sunset if I weren’t alone and had known the way down. Will try to come back for the sunset next time!