Tourist attractions in Takamatsu are actually visited quite quickly. Yashima, located not far from the city, offers an interesting perspective on the region and the Seto Inland Sea. It's one spot you'll have to check if you intend to stay in Shikoku.
To get there, take a train from Takamatsu station via JR line (compatible with Japan Rail Pass) or Kotoden line. Once in the small rural station of Yashima, you'll have to get on a twenty minutes bus (100 Yens) to reach the summit of the mountain. Be careful, because the bus goes once per hour on average, so plan out your trip before arriving in and out.
In the past, a cable car allowed you to climb, but it was closed in 2004.
Once at the top, you can walk around Yashima mountain summit through temples (some of which are part of the famous "Shikoku pilgrimage of 88 temples"), shops and even an aquarium. We didn't enter it because our visit to the Osaka Kaiyukan aquarium dated only a few days back.
And... that's it! After about 45 minutes, we're already back to the parking lot where the bus arrived. I must confess that I couldn't believe it. And yet, we didn't rush, like, at all: we visited nearly all the shops and stopped at the views to take pictures.
It was a bit tight for us. So we chose to leave the "public" path and go venture into the trails on the other side, much less visited. We saw incredible scenery, which looked like it was coming from a 7th season of Lost, with abandoned or crumbling buildings and cemeteries hidden in the forest. Surprisingly, it was almost more fun than the "public" side of Yashima.
How to get to Yashima
By train -- From Takamatsu Station, take the JR local line towards Tokushima (one to two trains maximum per hour) or Kotoden line and stop at Yashima station (15 minutes / ¥220 (~US$ 2.00)). Then take the Yashima Sanjo bus (one every hour) to the top of the mountain (20 minutes / ¥100 (~US$ 0.90)).
By car -- The toll costs ¥630 (~US$ 5.60).
Location unreachable with the JR Pass
Get there with a rental car
Museum : ¥500 (~US$ 4.50)
Aquarium : ¥1,200 (~US$ 10.70)
Open every day from 9am to 5pm
Aquarium: last entry at 4:30pm
How long / when to visit
Allow half a day or so