Shimonoseki and Kitakyushu

Shimonoseki is the westernmost city on the island of Honshu facing Kitakyushu, the northermost city on the island of Kyushu, right across Kanmon strait. The important location had left a lot of historical marks in the both cities.

City of Shimonoseki
Also called "Fugu capital", because of its largest fishing of pufferfish in Japan with restaurants offering Fugu all around the city. 
The location of Shimonoseki at the southwestern tip of Honshu island has given it historical importance, especially with the Bombardment of Shimonoseki in 1864 leaded for opening the port to foreigners, and also Treaty of Shimonoseki in 1895, when the defeated China handed over Taiwan to the victorious Japanese. An Imperial decree in July 1899 established Shimonoseki as an open port for trading with the US and the UK.

Kanmon Pedestrian Tunnel
Kanmon Pedestrian Tunnel, 780m in length, is opened in 1958 especially for pedestrians and cyclists. It's reachable by elevator, going down 60m under the ground, and allows you walking 15min between Honshu and Kyushu islands under the sea. For pedestrians it's free, and for cyclists it's expected to put 20 yen in a metal box at the entrance. For tourists there's a half stamp at the both ends, so don't miss to collect both. 
- admission: free for pedestrians, 20 yen for cyclists
- hours: 6:00 to 22:00

Karato Market
If you wanna try the local fugu fish or fresh sushi, this is what you need. The price for a piece of sushi is around 100-200 yen and you can choose from the plenty variation of fishes. On the second floor you'll find tables to eat the fresh food and to enjoy the view over the market.
- hours: Mon-Sat 8:00 to 15:00, Sun & National holidays 8:00 to 15:00

City of Kitakyushu

Moji Port

Located at the northernmost of Kyushu island at few hundred meters across the main Honshu island, Moji port was designated in 1889 as a special national port for exporting products such as coal. The port also made an important contribution to the modernization of Japan and served an important role during the Sino-Japanese War. With its locational advantage of being close to China, it made a rapid development since its opening until the begging of 20th century, when gradually went into decline.
Nowadays Moji port attracts 2mln tourists annually with its old western architecture and nice atmosphere. 

Kokura Castle
Kokura Castle was built by Hosokawa Tadaoki in 1602. It was the property of the Ogasawara clan between 1632 and 1860. The castle was burnt down in 1866 in the war between the Kokura and Chōshū clans. The keep was reconstructed in 1959.
An interesting fact is that Kokura was the backup target for the "Little Boy" bomb on August 6, 1945, so if Hiroshima had been clouded over, the first atomic bomb would have been dropped on Kokura. Then the city was the primary target for the "Fat Man" bomb on August 9, 1945, but on the morning of the raid the city was obscured by clouds and smoke, therefore the bomb was diverted to Nagasaki.
- admission: 350 yen
- hours: 9:00 to 18:00 (until 17:00 from November to March) 

Mekari observation platform

Located a bit lower than Moji ruins, it's worth walking up (~15min) viewing platform to enjoy Kanmon Bridge. One of the paths leading up is nearby Kanmon Pedestrian Tunnel, which connects Kitakyushu with city of Shimonoseki.