Places of interest close to Hiroshima

I have been invited to stay with a friend in Hiroshima for 3 weeks in November. I know the main tourist sites like Memorial Park etc., but can anyone suggest 'day trips' I could take by train or bus from Hiroshima to fill in some 'week day' times. Perhaps other towns of interest,I'm a good walker and like to explore etc. My friend will be working day times so not able to drive me around except for evenings and week-ends.. I'm thinking like 1 to 2 hours away from Hiroshima? Thank you.

Some recommendations:

Onomichi:
http://www.japan-guide.com/e/e3475.html

Tomonoura:
http://www.japan-guide.com/e/e3432.html

Iwakuni:
http://www.japan-guide.com/e/e6175.html

Matsuyama:
http://www.japan-guide.com/e/e5500.html

Bring some rabbit chow to Okunoshima (aka "Rabbit Island") and make friends with hundreds of wild bunnies. (From central Hiroshima it's 75 minutes by train to the nearest station, then you take a ferry.)
http://animalcafes.com/v/25558.html

Of the places mentioned by Uji; Iwakuni and Onomichi stand out to me. Mastuyama will require a ferry ride to Shikoku Island.

If you enjoy cycling too, you may want to do the Shimanami Kaido:

http://www.japan-guide.com/e/e3478.html

The ferry ride to Matsuyama is pleasant, and the Castle and Dogo Onsen are wonderful.

Hiroshima in centrally located inside the Chugoku. And Ideal to make as a home base.

As above, there are may locations that can be done as day trips. Not enough to fill 3 weeks though. But if you could do an overnighter somewhere once in a while. Then the whole region really opens up to you.

Some options not listed already is the Nishikicko Railway from Iwakani to Nishikicko, along a winding river with beautiful scenery.

Yamaguchi and Tsuwano are a very short trip away.

Fukuoka is 60 minutes away by shinkansen. Easily a day trip.

Nagasaki and Beppu/Yufuin are probably overnighters, as they'll take 3 hours one way to get to.

Not much to add to what has already been said. I adore Onomichi & visit whenever I can, Iwakuni is nice Although I didnt make it up to the castle. I would only add Kure for the Yamato and JMSDF Kure Museums. Useful if the weather is wet. Also I enjoyed wandering round the historical area in Takehara.

If you are coming in on a tourist visa consider getting a Rail Pass- then so many more place open up to you for day tripping.

Hiroshima to Shin-Osaka 91mins; H to Kyoto 122mins; H to Himeji 61 mins; the list goes on- how I love Japan and it's awesome public transport infrastructure. I wish I could meet the genius behind the Rail pass for tourists- it's a brilliant way to see the country.

Miyajima
http://traveljapanblog.com/wordpress/tag/miyajima/

A million thanks to all of you...Much appreciated!...I will follow all your suggestions...as my friend works daytimes, we are together in the evenings, but i now have much exploring to do and i love the train system!...Thank you!