תודה
Unfortunately I don't know about treks in this area, but, as far as I know Russia, where I have traveled a lot, eastern part of it is not touristic at all. It means, that it could be very difficult to find any option of independing traveling, or, at least tourist infrastructure However, you can easily make treks and trips around Baikal lake, Buryatia region, Sakhalin and Kamchatka. In this area tourism exist, good connnections, hotels/camps and so on If you can understand cyrillic, you can find a lot of material about traveling in this area, because local do make these trips and write their stories online Of course, you can try to find many spots independently, but, take into account, that sometimes distances are great, no roads, no hotels and etc. About border crossings. I check in the goverment websites, and they write, that there are several points of entry to China, that open to foreigners: Blagoveshensk/Haikhe, Habarovsk/Zhuantsy, and two more near by Vladivstok The problem is that part of border crossings are opened for locals only About China - get your visa in advance, because chanese do not obtain visas on arrival, and it could be problematic to get on in chinese consulates in Moscow, Habarovsk and Vladivostok Russians do not need a visa to China, if they travel in group, so, don't trust on what some can tell you in russian travel agencies