Dalian and Lushun, combined and abbreviated as LuDa which tucked away down the frontier of Liaodong Peninsula, is one of the miniatures of Chinas humiliation suffered from imperialists invasion in modern history.  The greedy neighbors, Japan and Russia, had long coveted the naturally-built harbors of LuDa.  In Sino-Japanese War of 1894, Japanese marines captured Lushun (The bestial Japanese soldiers committed a long forgotten war crime there; they slaugtered almost all of the inhibitants of Lushun then: over twenty thousands. I learned this masscre in high school.), and forced Qing Dynasty to concede the peninsula to Japan in truce agreement.  But soon Japan gave up its "loot" due to an international intervention led by Russia, so the begrudged Japan had to wait with deep rancour, and couldnt do anything but let Russia "borrow" LuDa from Qing government later and enclosed whole pennisula into its sphere of influence. 

Ten years later, Japan fought back.  The incompent Qing was forced again to "neutralize" the pennisula and let it be the battlefield of Russo-Japanese War in 1904-1905.  The fiercest fighting took place at 203 Hill, a stronghold that located at a small hillside dierectly facing and controlling Lushun Harbor.  It was a Pyrrhic victory for Japan, but the battle had become an classic exemplar of bravery and royalty for Jap soliders to copy.  To China, 203 was absolutely an indelible mark of an atrocious banditry between two imperialists on China land at the sacrifice of Chinese people and interest, and we shall never, ever let it happen again.  (If Japan dares do it again, China will definitely settle all scores with Japan once for all, and Japan knows that.)

P.S.  There is also a memorial prison, built during Russian and Japanese colonial period.  The Korean patriot An Jung-geun, who successfully assassinated Japanese prime minister Ito Hirobumi at Harbin in 1909, was executed in the prison.  FYI, Chinas Mainland built a memorial hall at Harbin to commemorate An in 2014.