There are tons of flowers and lots to do. The Kawachi Fujien has already been mentioned. There are many other places as well. Many cities have botanical gardens, there is also Kuju Flower Park in Oita and the Nokonoshima Island Park in Fukuoka:
https://www.youtube.com/watch?v=H-RmFcmhs9cThere are countless scenic and historic sights also. Kyushu is famous for its hot springs - including Kurokawa, Beppu, Yufuin, Takeo, and Futsukaichi. Beppu also has its Hells Tour and nearby monkey park/aquarium:
https://www.youtube.com/watch?v=K2NNi8MLcXMhttps://www.youtube.com/watch?v=zepPfkuqhokKumamoto has its castle, beautiful Suizenji Garden, and Mt Aso (closed at the moment):
https://www.youtube.com/watch?v=K9xyXmU8U1ghttps://www.youtube.com/watch?v=Tyh_nKrv5tYKagoshima is great to see the live Sakurajima volcano, hiking, and hot sand baths such as on Ibusuki. Plus the Senganen garden has a superb backdrop view of the bay and the volcano. See:
http://www.kagoshima-kankou.com/for/https://www.youtube.com/watch?v=LxDmLuq6ssIhttps://www.youtube.com/watch?v=lpnDK_Wux9QFor Fukuoka, there are many open parks, shopping, seaside historical areas, and urban neon. See this site as a good guide:
http://www.thejapanfaq.com/fukpic.htmlIt also has the Nanzoin Temple Great Buddha which is a hidden gem that few have discovered:
https://www.youtube.com/watch?v=lT4VQFmHFyMThere are also many useful videos to give you a preview:
https://www.youtube.com/playlist?list=PL7LcPcmoSg-j4RLa6iC7ayvBAbOn8-0...In terms of history and varied points of interest, Nagasaki is really the most interesting city on the island. It is worth a couple days to see the city, and another day to see areas nearby like Shimabara/Unzen or whatever interests you. Gunkanjima, while it takes 3 hours, will blow your mind.
http://www.ngs-kenkanren.com/eng/http://www.at-nagasaki.jp/foreign/english/http://www.youtube.com/watch?v=QdWRyHGW3rkBe sure to see Mt. Inasa at night if the weather is clear, and try the Nagasaki chanpon and saraudon! Also the Koshibyo temple is an often overlooked shrine that is quite unique in Japan:
https://www.youtube.com/watch?v=Mu_JnkVInTUSaga is mostly mountains, and famous for Arita pottery, Takeo onsen, and Karatsu seaside castle. If you're not into porcelain than you can skip it.
Plus Miyazaki has some very pleasant beaches, and its Takachiho Gorge is remarkable (but you can't get there by rail).
http://www.miyazaki-city.tourism.or.jp/en/http://www.kanko-miyazaki.jp/english/https://www.youtube.com/watch?v=H49x41ViFJkLastly if you have time, Kitakyushu has a few sights of interest also. It's Kokura Castle is one of the better ones, the view from its Moji wharf and preserved buildings are quite historical, and the view from atop Sarakurayama is one of Japan's best and rarely mentioned:
https://www.youtube.com/watch?v=Hl1pCW9IbbkFor comprehensive info on Kyushu, see:
http://www.visitkyushu.org
