Karakorum

While the Mongols were primarily nomadic peoples who didn't establish permanent settlements, Karakorum eventually became the site of the imperial ordu (literally a "collection of traveling tents" but later used by Mongolic and Turkic peoples to refer to settlements) where the main Khan held courts and received tributes. Since the vast majority of the "buildings" that made up the imperial ordu were felt or animal skin tents that could easily be moved, there aren't many physical remnants of buildings.

The region around Karakorum was the site of capital "cities" for numerous nomadic polities, including the Göktürks, the Uighur Khaghanate, and the Xiongnu, before becoming the site for the Mongol capital. William of Rubruck, a Flemish missionary, visited the site in 1254 and left accounts of the city and of the Khan, which are the best extant primary sources describing what the city was like. By the time the Mongol Empire was partitioned into four quadrants (the Golden Horde, the Ilkhanate, the Chagatai Khaganate, and the Empire of the Great Khan/Yuan Dynasty China), Kublai was the Khan who ruled over Karakorum, but after the defeat of Song China the capital was moved to Shangdu (the Xanadu of Marco Polo's travels) in China proper and Karakorum became nothing more than a simple provincial administrative center before fading into myth and obscurity. Karakorum was later decisively destroyed by Xu Da, a Ming-era general who took control of the town and destroyed it purely out of spite.

Karakorum, being the seat of Mongol political power during the height of the empire, was most likely the site where Tibetan Buddhism was introduced to Mongolia proper. The Erdene Zuu Monastery in/near Karakorum is the oldest Buddhist monastery in Mongolia, and was built by reusing stones from the ancient site of Karakorum.

• 🌍 Xar Bulgas (Har Bulgas, Khar Bulgas). Ancient capital of the Uigher Empire (800 AD). Exit Harhorin to the west, at the west side of the town, the road turns NW and crosses the Orhon River. This is a paved road. Then there is a section of unpaved road then paved again. The pavement ends the second time at about 13.5 km from Harhorin, there are mileage posts. Take the eastern (right) most track, generally go north past the Herder's Gers. At this point the road is going NW, continue to N47 23.946 E102 36.092. Turn right going NE. N47 25.838 E102 39.506. 
• 🌍 Khushuu Tsaidam Museum (in Harhorin there is a paved road on the west side of the Erdene Zuu Monastery; this road leads north to the museum, about 45 km). This museum is funded by the Turkish Government. There was an old Turk Empire located here and two stone stele with Turkish inscriptions to Bilge Khaan and Kul Tigin. Bilge Khaan lived 683-734 CE. There is a caretaker living on the north side of the museum who will let you in. 

• 🌍 Bilge Khaan Memorial. daytime. 

• 🌍 Kharkhorum (Harhorum, KharaKhorum) (take main paved road west from Ulaanbaatar; at Lun, the road splits you can take either branch, but most take the southern branch; if you take the southern branch the road is paved all the way, except for a 50 km section east of Lun). The capital is located on the north side of the Erdene Zuu Monastery. Go to the northwest corner of the Monastery, enter the fenced compound, used to be a sign here stating that the UN had paid for the fence. About 100 m north you will come to some small fenced areas and a stone turtle, one of two inside the city fence. Between the turtle and the stupa is the remains of Ogodei Xaan's palace. A German and Mongolian team has been excavating here. The other stone turtle is in the SE corner. A third is in the hills south of Erdene Zuu. 
• 🌍 Erdene Zuu Monastery (Erdenezuu) (just outside town of Kharkhorin, to the north of Kharakhorum Museum). Daily. This monastery was built in the 1500s, but has been destroyed several times. It is free to enter the grounds, but a tour inside the old temples costs 3000 ₮, 5000 more to take pictures inside. In the NW corner is an active temple serving the local population, this temple is in Tibetan style. none. 
• 🌍 Tövkhön Monastery (Tovkhon Temple), SW of Harhorin (from Harhorin go south, upstream on the west side of the Orhon River). Daylight. Go southwest from Harhorin on the west bank of the Orhon River to N46 56.000 E102 22.322 turn right (west) There is a park entrance with US$3 fee per person. Continue up the valley until you see the many blue cloths turn up the hill on the SW side. The upper part of the road is in poor condition. Alternately, from the Orhon Waterfall, go NE along the river until you come to the bridge at N46 48.503 E102 1.668 follow the river on the west side to the turn mentioned above. Great view from the top. USD3. 
• 🌍 Orhon Waterfall (Orkhon Waterfall), SW of Harhorin (southwest from Harhorin, the west side of the Orhon River). Southwest on the west side of the river to the bridge at N46 48.503 E102 1.668. Cross to the south side and continue west to the falls at N46 47.151 E101 57.648. 
• 🌍 Kharkhorum Museum (Kharakhorum Museum). Dedicated to exhibiting artifacts from the Mongolian history. 

• Anyone who's interested in steppe history and/or the history of the Turkic peoples should visit Khar Balgas to the northwest of the city. Here was the ancient capital of the Uighur Khaganate, and across the river a short distance are the Orkhon inscriptions, which contain the earliest recorded Turkic writing.
• Horsetrails, Uvurhangai Aimag, Harhorin Sum, Erdene Zuu St. (From Erdene Zuu, go west about 2km), ☏ +976 99242980. Horse trips through the countryside near Xar Xorin (Har Horin, Khar Khorin) 

During the summer, there are several restaurants in the shopping area. The white hotel between Erdene Zuu Monastery and the shopping area, on the North side of the canal serves meals.

Several small cafes were open during the day near the container shopping area 1.5km west of the Erdene Zuu monastery.

• Morin Jim, Uvurhangai Aimag, Harhorin Sum, Erdene Zuu St. (From Erdene Zuu, go west about 2km), ☏ +976 99242980. 7am - 10pm. Guesthouse and Cafe. Grilled Chicken, Mongolian Connected with Horsetrails tour agency US$3-5. 

There are several Hotels, guest houses and ger camps.

• Morin Jim Guesthouse, Uvurhangai Aimag, Harhorin Sum, Erdene Zuu St. (From Erdene Zuu, go west about 2km), ☏ +976 99242980. Bed in shared ger (yurt). Clean, outhouse, no shower. See the webpage for local horse trips. $8. 
• 🌍 Ikh Khorum Hotel, Restaurant ("Их Хорум" Зочид буудал, ресторан), in Kharkhorin, ☏ +976 70327007. Modern hotel out on the steppe with restaurant/bar, free breakfast, wifi, hot tub. (updated Aug 2020)
• 🌍 Family Guesthouse, in Kharkhorin, ☏ +976 96458188. Establishment with yurt accommodations, fire pit, and some food. On north edge of town. 66 ₮. (updated Aug 2020)
• 🌍 Gaya's Guest House, Kharkhorin (south side of town), ☏ +976 99893809. More yurt life. Open, neat common area (dining room, bar). Friendly host. Wifi and shower. (updated Aug 2020)

Get a shared car or jeep, or minivan to Ulaanbaatar, Hujirt, or Tsetserleg from the east side of the Container marketplace in the middle of town.