Central Armenia includes the marzes of Aragatsotn, Ararat Marz, Armavir and Kotayk.
This is the heart of the nation, with Yerevan at its center. Much of it is comprised of the Ararat valley, which is flat and dry most of the year, and provides spectacular views of Mt. Ararat on a clear day. The valley was split in half after a Turkey invaded shortly after WWI, and the border is still a sensitive area, with Russian troops and bases guarding the Armenian side.
As with the rest of Armenia, Armenian and Russian are pretty much universally spoken, while English, French and German are spoken by few. English is of course gaining in popularity.
Most tourists arrive in Armenia at Zvartnots International Airport, in the middle of this region, and stay in Yerevan.
Day trips can get you anywhere quite easily. There are plentiful cheap, guided day tours offered by tour agencies all over Yerevan to place like Khor Virap, Garni/Geghard and Echmiadzin/Zvartnots. You can also hire taxis for 100dram/kilometer (30 US cents) and about 1,500/hr ($5) for waiting time if you want to do things at your own pace. Car rentals are more expensive, but useful if you want to strike out on your own into Khosrov Reserve or just explore the Hrazdan Gorge at your own pace.
West end of Central Armenia
Amberd Fortress and Byurakan Observatory and Church
On the southern face of Mt. Aragats, Amberd Fortress is a quick trip from Yerevan and a popular escape from the Yerevan summer heat. The fortress looms over a small church, and both overlook the Ararat Valley and Mt. Ararat across the valley. Further up the mountain is a nice lake which is the starting point for the hike up to the southern peak of Mt. Aragats.
Before reaching Amberd, the village of Byurakan offers the ancient church of S. Hovhannes. Tucked away behind some houses, it is marked with the old Christian cross used before the Armenian cross design came into use. The observatory in the same village was home to Viktor Ambartsumian, a famous astrophysicist, and offers tours during the day, or star gazing at night. Both are usually by appointment, though showing up and asking nicely has been known to work.
Ashtarak and Kasagh River Gorge monuments
The picturesque town of Ashtarak is less than half an hour from central Yerevan. It has 3 very old churches standing and 2 in ruins. It is also home to Ashtaraki Dzor Restaurant Complex - well worth a stop for a reasonably priced meal and nighttime entertainment show, all outdoors, and long popular with Armenians.
The northwestern parts of Kotayk are mountainous, forested and popular with Armenians as places to go and relax. Hankavan, Tsaghkadzor, Bjni and Aghveran are all well known by Armenians as places where nature is nice, and relaxation is possible not far from Yerevan. Each place has different things to offer, but all offer hills, mountains and forest.
Garni Temple and Geghard Monastery
These are absolutely obligatory stops for any visitor to Yerevan, for good reason. Garni, a small Roman temple built in the first century by the Armenian king is incredibly sited atop basalt cliffs, and has a ruined bathhouse and the foundations of a temple in the fortified compound as well.
Arguably the most awe-inspiring site in Armenia is the 11th century Monastery of Geghard, much of which is carved out of the solid stone of the mountain it abuts. Once housing (and still named after) the lance that pierced Jesus' side, it is sited at the end of a canyon, surrounded by steep rock mountains, with fortified walls, holy springs, an upper chamber with unparalleled acoustics and many intricate khachkars.
Sardarapat Monument and Museum
Most in the Armenian Diaspora know the famous song Sardarapat about the battle fought here which saved Armenia from complete annihilation by Turkey after WWI. The monument is large and looks out over today's border with Turkey, drawn after that battle. Adjoining is Armenia's largest ethnographic museum, with a large collection of artifacts from different parts of Armenia. Well worth a visit if you like to see how people lived back in the day.
The Cathedral of Echmiadzin, founded in 301 by St. Gregory the Illuminator and rebuilt and added to for over 1,700 years now is the heart of the Armenian Church, and seat of the Catholicos of all Armenians. The altar is built over an ancient pagan fire worshiping pit (accessible from the museum behind the altar), the inside has some interesting frescoes, altar, lamps, and thrones. The intricate bell tower entrance is an addition from the 1800s, and the surrounding grounds have gardens with examples of khachkars from throughout Armenia and further. Near the new entrance gates are a few exquisite khachkar examples from Jugha (now in Azerbaijan) - which had by far the largest khachkar collection in the world. The thousands of khachkars which remained there were destroyed during this decade by the Azeri government.
Two other important churches in the same town, both honoring Roman virgins who were martyred for refusing to marry Armenia's heathen king are.
Deep in a pit at Khor Virap, Armenia's Christianity began. Imprisoned here for his heretic faith, St. Gregory the Illuminator was not released until he cured Armenia's king of a terrible disease (some legends say he had turned into a boar). The king, in gratitude converted himself, and Armenia with him, into the first officially Christian nation in the world. The fortified monastery sits on a small hill in a very flat Ararat Valley. The view of the mountain is the best you'll get, though the monastery otherwise is not so remarkable. 45 minutes from Yerevan, this is an easy morning trip, or a quick stop along the road heading to Southern Armenia.
There are buses to and from Yerevan train station. As of Aug 2015, the last bus leaves Yerevan at 14:00. The last bus, which is a mini-van, from Khor Virap is 17:00. The fare is 400 Dram.
Other sites worth visiting
Outside of Yerevan, Central Armenia has a limited food selection to offer. Some of the bigger towns have restaurants or bistros, but outside of this and a small number of roadside barbecue (khorovats) joints, there is very little.
Drinks and sometimes bars are available where food is served.
Central Armenia is very safe for residents and visitors alike.
You'll never be more than an hour away from Yerevan, so you'll likely get back the same way you arrived.