Uyuni a small town situated in the middle of nowhere. It originally blossomed as a railroad junction, and even if this is still an important aspect, no doubt is tourism now its main source of prosperity. What would otherwise be a fairly dull stopover en route between Salta, Argentina and La Paz or Potosí, has become absolutely mandatory on this leg of the gringo trail. Sole reason: Salt flats, -the world´s biggest that is. (See Salar de Uyuni).
Plan to arrive a day or two before you intend to depart on a salt flat tour, especially if there are only 2 of you. That gives the chance to meet other travellers, thus a larger group has more bargaining power for the 'daily rate'.
Uyuni has a small airport (IATA=UYU, IACO=SLUY). Líneas Aéreas Canedo (in codeshare with Aerosur) flights Mondays, Wednesdays and Fridays from Cochabamba Jorge Willstermann Intl Airport on a Super DC-3 (an historical aicraft built in 1952). Those flights take about 90 minutes, and land at a salt runway, near the city (1km northwest). Ticket prices are 150USD one way, 250USD return. More information at Líneas Aéreas Canedo hangar (in Cochabamba Airport) or in any Aerosur office. (At 2008, flights cancelled while working at the Runway from Uyuni Airport).
You will need 12-15 hours from La Paz, by bus. The bus ride can be bitterly cold in winter - travellers have been known to sit in their sleeping bags on the night bus from Oruro to Uyuni. With two exceptions (Todo Tourist Bus and Panamerica Sur) you must change buses in Oruro to get to La Paz. Buses to Oruro/La Paz are often booked up in advance - you likely need to book at least the day before, several days if you wish to take the comfortable tourist bus or one of the better bus companies - best to do this before going on a Southwest Circuit tour (if coming from San Pedro de Atacama, be prepared to spend a night in Uyuni and have little choice of bus company).
There are several buses daily to and from Potosí (6-7 hours, 30 Bs.), from there you can go one to Sucre (3-4 hours more). Beware however, companies such as Transporte 11 de Julio have been known to cancel buses without notice, and without even opening their office to explain.
Many daily departures around 5:30 - 6:00 AM for Tupiza, stopping halfway for lunch in Atocha, 7-8 hours, 60 Bs. Three days a week there are 9 AM departures, and occasionally a Land Cruiser departs 6-7 PM, -ask around. Although the train is definitely smoother, and somewhat faster, this bus ride offers terrific views.
Trains run south to Villazon on the Argentinian border, stopping in Tupiza and Atocha. Northbound trains go to Oruro. Less frequent and less comfortable departures to Calama, Chile.
Museo de Arqueologia y Antropologia, Arce (Half a block from the clock tower). Quite a few skulls and a handfull of mummies, plus some less exciting stuff.Bs 2,50.
Despite its modest site and geographical isolation, Uyuni is worth an hour or so walking around. Particularly the Avenida Ferroviaria has many monuments, mostly railroad related.
Allegedly Bolivia´s first locomotive, stands in th emiddle of Avenida Ferroviario, by the corner of Calle Santa Cruz.
Train Graveyard - a couple of km south of town, by the railway to Chile, there are dozens of old, rusted locomotives, a few wagons and some other antiquated machinery. Usually a stop on salt flat trips.
The salt flats, Salar de Uyuni, can be visited on daytrips, or longer trips, up to 4 days, including a swipe down towards the Chilean border and the lagoon and geysers of that area.
Make sure that you point out that you only wish to go with a responsible driver; there have been reports of drunkenness among drivers that may be averted with continued pressure on the tour companies before departure.
Several blocks of the main street Avenida Potosi turns in to an open air market, selling a bit of everything, including loads of handicraft.
For a cheap lunch (10Bs for soup and main) head for any little joint with the sign Almuerzo outside.
Minuteman Pizza - Ferroviaria 60, Uyuni, 591 2 (693 3186)  Hours: Breakfast 7:30-10AM , Dinner 5-10PM Within the Tonito Hotel, backpackers congregate here in the evenings (note that locals may not be allowed). Large variety of pizzas (including spicy llama), great breakfast, English-speaking owner, travel-book library. From 30 Bs for an individual pizza.
Pub-Pizzeria-Restaurant ARCOIRIS – Avenida Arce 27, Uyuni, 591 2 (693 3177) ; English / Italian - speaking owner ( Willma ); Hours: 3-12PM; Pizza & Pasta (Italian taste), typical local plates, some time live music.
Have a beer during daytime at the shack right next to the clock tower.
Tonito Hotel, Ferroviaria 60, Uyuni, 591 2 (693 3186)  THE "high-end" hotel in town. Rooms are situated around an internal atrium area. Clean rooms, electric-heated showers, transportation from train station available, book ahead in the high season. Room heater available for rent for $3 US. 19 rooms. Breakfast Included. Double with private bathroom, $57 US.
Hostal Sajama, Potosí 35, 693-3099. Cheap place with basic clean rooms. Single with shared / private bathroom Bs.25 / Bs.40. NOTE! On May 30, 2007, two Canadian students visiting Uyuni were found dead in their rooms at this hostal due to carbon-monoxide poisoning from their gas heater. 
Hotel Avenida, Ferroviaria 11, 693-2078 , clean and inexpensive in the town center, near tour operators. Only two hot showers, but the door to one is often locked. Double/Matrimonial 60Bs (U$S 9), with bath 100Bs (U$S 14).
Beware of the cheap hostels near the bus offices. If you arrive in the early morning these places will charge you a full night for your stay until 12PM (noon).
Hostelling International Salar de Uyuni, Calle Potosí esq. Sucre, Uyuni. There are reports of poor service, unbelievable levels of rudeness and management not honoring bookings, in fact literally shoving booked guests into the street late at night..
Hotel Girasoles, Av. Santa Cruz 155, Uyuni, ☎ 026933323. 35$ double.
There is now a Banco Credito ATM in Uyuni, on Calle Potosí. Prodem gives cash advances on mastercard or Visa creditcards with a 5% commission. You can get cash out of an ATM indoors at a bank with Maestro
There are several casas de cambios to change travellers' checks or dollars, euros, Chilean pesos or Argentinean pesos. If you are heading to Chile, get rid of your bolivianos, as the exchange rate on the other side is much worse.
One of a handful of laundries, Laundry Huila Khota at Av Ferroviaria 257 (by the homonymous hotel), has same-day service at 8 Bs per kilo.
The cheapest international phone calls seem to be at Call Shop Uyuni, Av. Arce, 30 metres from the clock tower. Bs 2,50 to most of the world. Internet here is expensive, though, at 6 Bs an hour.
Get the exit/entry stamps you need at the immigration office at Potosí and Sucre.
There are several slow internet places for around 5 Bs. per hour.
Salar de Uyuni - with over twelve thousand square kilometers, is the largest salt flat in the world. It can be done as a daytrip, or with a few overnights, often combined with the lagoons and geysirs closer to the Chilean border. Instead of returning to Uyuni, you can opt for San Pedro de Atacama or Tupiza.
If you plan to go Chile, you can get transport onwards to San Pedro de Atacama instead of return to Uyuni. The price is usually around an extra $10USD. Remember to get an exit stamp in Immigration Office in Uyuni (the date on the stamp is the expected exit day, so you may get Chilean entry stamp with earlier date).The Immigration Office is open 7 days per week.