Lake Baikal. Located between Buryatia and Irkutsk Oblast, is the the deepest and oldest lake in the world and also the planet's largest body of freshwater.
Russian is understood and spoken by all; some members of ethnic minorities (especially the Buryat) are bilingual and speak their native languages with one another.
The Baikal Highway (Байкальский тракт), a route from Irkutsk to Listvyanka village usually taken by marshrutka. One-hour trip starts from Irkutsk reservoir and is 68km long. The road is in some distance from the Reservoir that can be seen by rare glimpses as the road goes up and down along the hills covered with pines, burches and bush.
The Circum-Baikal Railway (Кругобайкальская железная дорога), a memorial railway in Pribaikalsy National Park. It was a part of Trans-Siberian Railway in active exploitation till 1950s. When the main bypass was constructed the Railway lost its importance and is used now for tourist and emergency purposes. A few carriages depart from Slyudyanka, the southmost station and 4h 40min later arrive in Baikal station, wich is also a port up north. Enjoy panoramic views full of beautiful nature as the train moves along the shoreline. There are four stops and 38 tunnels during the trip. Retro trains (№988/987 Байкальский круиз) shuttle on special dates.
While being in woods, beware of snakes that are commonly warming in the sun on the stones. There is not many of them but some may be vipers.
The other problem of this (and other regions of the North Hemisphere) is ticks. Their bites may be infectious. Usually vaccinations are taken beforehand.
The Baikal-Amur Mainline, which runs on a parallel track to north of the Trans-Siberian, begins at Taishet in western Irkutsk Oblast and on to Severobaikalsk.