Lake Sevan Region is in Armenia, and it is the same as the Gegharkunik Marz of Armenia.
From Yerevan, once you get to Lake Sevan visit Sevanavank Monastery, then head south to Hayravank Monastery and Noratus Cemetery. If you'd like to explore further, you can continue on down to Vanevan Monastery and Makenyats Monastery, plus check out the towns of Kavar and Vardenis.
Lake Sevan is a popular summer beach destination and has many resorts, cabanas, fish restaurants and other amenities for visitors. Also, a main reason to visit is to see Sevanvank monastery, and other lakeside churches; most visitors come on day-trips from Yerevan.
Lake Sevan lies at 1,900 m altitude, twice that of Yerevan, and is fresh water, partly freezing in winter. The temperatures are significantly cooler than in Yerevan, and the winters much longer. This popular spot for a getaway in the summer is usually packed in July and August, when it's warm enough to enjoy the beaches and swim in the waters. Although Armenia is landlocked, this lake, which covers 5% of the country is vast, and much of it quite pristine, with some decent beaches.
In pre-industrial times the lake was much larger and deeper, but in Stalin's era it was drained unsustainably for irrigation and hydro-electric power, and its water quality and environs were degraded. It's now being rehabilitated and the water level is creeping back up.
Armenian and Russian are universally spoken. English, French and German spoken by a few, though English is gaining quickly.
If you just want to go to the "kghzi" peninsula with the most popular beaches during the summer, then marshrutkas make frequent trips from Yerevan for cheap. Throughout the year you can take the Ijevan/Dilijan/Noyemberyan marshrutka and hop off at the lake as well, or depending on where you want to go in the region you can take a van directly to Vardenis or Martuni or Kavar.
There is a train that can take you to the peninsula, and then continues around the top of the lake over to Shorjha, a beautiful spot. The train, while cheap, does not earn rave reviews.
There are many cars crossing the region. So, you will not have issues finding someone to take you as far as you desire. Always offer a little tip in return—the equivalent of a marshrutka ride is common.
Getting to Shorjha on the far side is trickier, and a taxi may be your best bet. You can get a taxi to the Lake with some time for you to enjoy the beach for about 10,000 dram round trip. Taking taxis around this area is not hard, but just stick to the established prices of 100 dram/km, and 1,500 dram per hour for waiting time.
Other destinations in the region include:
There are a number of excellent fish restaurants along the shore, especially just north of the kghzi peninsula. Barbecued fish is cheap (not the ishkhan trout though), and is always juicy. The fried fish is usually quite nicely marinaded and is also cheap. Crayfish (rock) are also found at these restaurants, and are worth trying. The crayfish and fish are also sold along the side of the roads, by little street vendors holding their hands apart.
Vodka
Armenians tell of drownings due to rip currents and whirlpools in the lake. Though this does not appear to be documented, and is more likely a result of a population that does not have much swimming experience, don't swim out too far alone.
Any bus or van heading south past the peninsula will take you to Yerevan and Central Armenia. You can also head up northwest to Dilijan and Northern Armenia, or Georgia.
Furthermore, you might want to catch a ride or hike into Nagorno-Karabakh (Artsakh).