Developing new markets is important for casino companies as China's corruption crackdown and a slowing economy curb revenues in Macau, the world's biggest gaming hub. October revenues in Macau fell 23 percent, the largest monthly drop on record.
Japan is seen as the biggest unclaimed prize, a market that research firm Union Gaming estimated would generate $15 billion in annual revenues, more than double what Las Vegas recorded last year.
Read More US casino billionaires place bets in Japan
South Korea, by contrast, generated $2.4 billion in casino revenues last year, less than half of Vegas revenues and just 6 percent of Macau's take.
That tally will grow as new casinos open. The main draw is Chinese tourism. Arrivals into South Korea from China rose about 53 percent last year, with some tourists signing on for triple packages that include cosmetic surgery, shopping and gambling.
"South Korea already has got the gaming industry infrastructure," said Ben Lee, managing partner at IGamiX Management & Consulting Ltd, a Macau-based gaming consultancy.
"At least they are familiar and don't have to go through the initial stages like Japan."
Read More Can South Korea become the next Vegas or Macau?
South Korea's first gaming-and-entertainment integrated resort, Paradise City, broke ground on Thursday and is expected to open in 2017. Joint venture partners Paradise Co Ltd and Sega Sammy Holdings Inc plan to invest about 1.3 trillion won ($1.17 billion).
Hong Kong-based Chow Tai Fook Enterprises, owned by Hong Kong tycoon Cheng Yu Tung, has signed a letter of intent to invest more than $1 billion in a resort in Incheon where Paradise City and U.S.-based Caesars Entertainment Corp are building.
Sands wants in, too.
CEO Sheldon Adelson said last month he was visiting South Korea as part of an Asia trip with stops in Macau and Japan, and boasted of designing "the most iconic building in the world" in South Korea to house a casino and entertainment complex.
He did not specify a location but Sands' head of global development, George Tanasijevich, was quoted by South Korea's Yonhap news agency as saying the firm was interested in Seoul.
Indeed, South Korea was mentioned 14 times during a Sands analyst call in October, according to a transcript from Thomson Reuters' StreetEvents. During the previous quarterly call in July, when Japan's gambling prospects looked more promising, Korea came up only twice.
Read MoreNew border rules may boost Macau casinos
Adelson sees one big obstacle: South Korea will allow only foreigners to gamble at large resorts. Locals are allowed to play in only one casino, which generates more revenue than the other 16 casinos combined.
Adelson has been vocal about wanting to see that changed.
"We are not interested in foreigners-only resorts," he said.