One of my main investing themes is to seek ways into frontier markets before the mainstream investors show up. We did this in Myanmar with Yoma and that worked out well. Getting in early was the whole point of my trip to Mongolia several years ago and that has worked tremendously.
One of the last closed markets is North Korea (OTC:DPRK). Many forward thinking investors such as Jim Rogers have described the hermit kingdom as having excellent long term prospects. In fact Rogers expects the North and South Korea to eventually merge which would create a powerhouse in his view.
Mongolians have already developed a relationship with North Korea and there are many North Koreans working in Mongolia. A small company in Mongolia named HBOil recently inked a deal that gives the company a foothold in North Korea. BDSEC in Mongolia recently did a write up of the deal and issued a buy recommendation. HBOil trades on the Mongolian Stock Exchange for about $.30 USD per share. Here is a link to the report. I own shares in HBOil and intend on buying more. This is a long term share holding in the 5-10 year range.