Hiroshima to Shimonoseki

Hello everyone!
After spending a few days in Hiroshima I will be going down to Shimonoseki and into Kyûshû. I have a few days spare and would like to explore the area between these two places with this time!
I will of course be going to Iwakuni as well as Yanai (Old district and a few museums, as well as the kofun) and Hofu (Hōfu Tenman-gū,
Suōkokubun-ji and Mori Museum + Gardens). I would like to stay along the Sanyo Main Line and the Ube Line, i.e. next to the coast and would love any suggestions on what to do around there! Islands are also welcome though!
Thank you.

I would walk from honchu to kyushu on the underground walkway. Nothing spectacular but it is "I done it!" kind of a thing.
Also I would rather spend the time in places like Kumamoto or Nagasaki.
Taking the ferry from Hiroshima to Beppu and then working towards Fukuoka is one way to enjoy the coast, wild, and hot springs.

The area around Yamaguchi is more interesting than Shimonoseki.

Looks at this site to see the places to visit.

JH, I will be going to all those places later on! But thank you all the same for the recommendations :)
Hakata14, of course I�fve already checked this site first but it doesn�ft have much information :) I�fm interested in what there is to see along the coast between Hiroshima and Shimonoseki because it seems like an area nobody ever goes to and I�fm sure it has some interesting things to offer!

You didn't mention if you have seen Miyajima before, but if not, that is the pièce de résistance of the Chugoku region.
https://www.youtube.com/playlist?list=PL7LcPcmoSg-iCNZ6AdsKGUB-HPKNxP1...

Iwakuni is an excellent place to explore too, and does not take that long. And while it does take an hour's bus ride from Yamaguchi Stn, the Akiyoshido Limestone Cave is a stunning natural wonder over 300 million years old with huge caverns and an underground river - the 1km walk through it is something unique and unforgettable.
https://www.youtube.com/watch?v=DqIKC9S8TFQ

Shimonoseki is sadly given short shrift in many guides. When the weather is clear, going up to Hinoyama gives an excellent view, the fish market is interesting enough (and if you want to try fugu, you're in the right area), the aquarium is actually quite impressive, the Chofu area has a lot of old samurai related homes, gardens and related temples, and yes, if you want to walk under the sea down the Kanmon Tunnel, you can do that too.
https://www.youtube.com/watch?v=6y4K6erVyvA

Kitakyushu has a few sights as well - Kokura Castle is not bad, the Moji Retro area is like walking back 100 years, and the view from atop Sarakurayama is a secret gem that only the most well informed know about.
https://www.youtube.com/watch?v=Hl1pCW9Ibbk

Fukuoka is the nest closest big stop,
http://www.thejapanfaq.com/fukpic.html
https://www.youtube.com/playlist?list=PL7LcPcmoSg-j4RLa6iC7ayvBAbOn8-0...
But yes, Nagasaki is really the most interesting and varied city on Kyushu.

Hakata14, of course I�fve already checked this site first but it doesn�ft have much information :) I�fm interested in what there is to see along the coast between Hiroshima and Shimonoseki because it seems like an area nobody ever goes to and I�fm sure it has some interesting things to offer!Indrustrial factories, farmland, shipping ports etc.

Google map it. The reason it doesn't come up much. If unless you are into factories, ports, stainless steel pipes, rice fields etc.

Ken gave a lot of good ideas for southern Yamaguchi Prefecture, which is where you want to visit.

Some repeats, but:

-Ube - Sorinji Temple has a nice temple garden and there are some museums and other sites to keep you busy.

-Chofu (in Shimonoseki) - famous garden and samurai residences

-Suo-Oshima Island: Haven't been there. There are some sites, but it seems that the atmosphere is really the reason to go:
http://www.suo-oshima-kanko.net/kanko.html

-Akiyoshido Cave - Not technically located along the Sanyo Line, but there are buses that go there from Shin-Yamaguchi Station.

-Shunan actually has some sites, but many are not convenient without a car. Many of the towns have interesting sites, but it depends on your interest and how impressive the sites need to be for you to visit. You could make a slight detour into Yamaguchi City, as well, which is a nice daytrip.

(I know you've asked for places on the coast BEFORE you get to Shimonoseki, but) one thing I'd highly recommend if you get to Kokura is to go to the TOTO toilet factory museum.

I'd also recommend Tsuwano. The old town and inari shrine there are awesome. Take a train inland from Shin-Yamaguchi for about 1 hour.

I you stay near Shin-Yamaguchi station, you can access a lot of the nearby sites via train and bus. Somebody already mentioned the caves for example.

Thank you hakata14, Ken, Rabbityama and Winter Visitor for the answers!
Yes, I will be going to both Iwakuni and Miyajima before heading down, they seem like beautiful places.
I�fll be staying 2-3 days in Shimonoseki itself since there is a lot to do (including Ganryūjima), but also to rest a bit from the first leg of my trip before going into Kyûshû.
I�fve actually already been to Hagi, Masuda, Tsuwano and the caves on a previous trip! But I might go up to Yamaguchi itself this time since it isn�ft that far away from where I want to go.
I�fve also added Otsukushima to my list. Does anyone know of any bike rentals in Shunan, and could I take the bike on the ferry to the island with me? If not I�fd just have to stick with walking.
I�fm really interested in anything (partying, shopping and nightlife excluded), so I�fm perfectly happy with sites that aren�ft that impressive.

I�fm very excited already!

PS: I'll also be going to Ube and Chofu, thanks for the recommendation!

If you are going to Ube, you might like Tokiwa Park.
http://bit.ly/1Te8Iaq

Especially if you like swans and pelicans.