The word "Viking" was originally a verb, describing the action of seafaring, and so applies only to Scandinavians who were seafarers, not necessarily all Scandinavians.

The ancient Vikings navigated by depending on the instincts of birds. They took on board several ravens, releasing them one at a time as they sailed westward. If the raven flew back along the course from which it had come, the Viking ships continued due west. But when a raven flew a different way, the ships would change course, following its flight path in search of new lands.

Due to Iceland's geographical isolation from mainland Europe, no-one had ever set foot on it until mediaeval times. The first humans to arrive on Iceland were Irish explorers, who arrived no later than the year 795. The colony that they established did not last; when the Vikings arrived eighty years later, only a few hermits remained. (source)

In the ninth century, Vikings (known as Varangians in the East) were raiding Constantinople, at the mouth of the Black Sea. These expeditions were launched from Kiev via the Dnieper River.

St. Edmund the Martyr (841–869), King of East Anglia, was killed at the hands of the Vikings, either by undergoing the blood eagle rite (having his ribs pried open to expose the still-breathing lungs) or by being whipped, shot through with an enormous number of arrows, and being decapitated (source)

Dublin was founded by Viking raiders in the ninth century.

In a single raid on Britain around the year 1000, the Vikings used a fleet of eighty "dragon ships", each carrying 100 soldiers. (source)

To encourage his fellow Norsemen to settle a large, snow-covered and ice-covered island he discovered in the year 982, Eric the Red called it Greenland. A few years later, twenty-five ships filled with eager settlers sailed for Greenland. (source)

The Vikings founded a settlement in North America almost 500 years before Columbus "discovered" the New World. In the year 1000, Leif Ericson, son of Eric the Red, sailed from Greenland on an epic westward voyage that took him past "Helluland" (likely Baffin Island) and "Markland" (likely Labrador) to a land called "Vinland" (modern-day Newfoundland). The Vikings later founded a colony on Vinland, near what is now the fishing village of L'anse-aux-Meadows. However, the Vikings soon discovered that the lands were already inhabited by "Skraelings" (likely Inuit), who were often hostile. After a few years, the first European colony in the New World was abandoned and the colonists sailed home. (source)

In the year 1000, the world's largest slave market was run by Vikings in Dublin.

The replica Viking houses at L'anse-aux-Meadows settlement, with their stone foundations and turfed roofs, are significantly more permanent than the original buildings built there, and have already been in use longer than the original buildings were in use. (source)

When Viking Leader Harald Hardrada invaded England in 1066, he quickly defeated the northern militia near York and waited for the big showdown with King Harold II who was on the south coast anticipating a Norman invasion. Not expecting the English troops for days, Hardrada and his men camped on meadows on both sides of the River Derwent at Stamford Bridge and, as it was a nice day, many removed their armour and indulged in some sunbathing. They didn't even rouse themselves when they saw approaching soldiers, presuming them to be a detachment of Vikings. By the time they realised it was the English army, it was too late. The Vikings were overwhelmed and Hardrada was killed.

Vikings were used as guards by some Byzantine emperors.

The Icelandic language is remarkably similar to Old Norse. Icelandic schoolchildren have no difficulties reading the Eddas and the sagas, the great epics written in Old Norse. (source)

Russia can be seen as having been founded as a by-product of Viking slave raids in the ninth century. (source)

Viking ships were steered by rudders on the right side, which the Vikings called styrbord, Old Norse for "steer side", from which the English word "starboard" comes. The Vikings docked their ships on the left side, which they called the ladebord, the "loading side". This eventually became the English "larboard", which sounded so much like "starboard" that it caused problems. Eventually, the British Admiralty ordered that the left side be known as the "port" side. (source)

The Vikings established a colony on the southwestern coast of Greenland that lasted around four centuries, from 982 to nearly 1400. The colonists routinely sailed to North America to get wood, as there were no trees on Greenland, long before Columbus "discovered" America. In the late 1300s, the Black Death ravaged the colony, Eskimos attacked, and the climate grew colder, and the colonists finally either died out or left. (source)

The worst possible death for a Viking chief was to die peacefully in bed.

Only one Viking helmet has ever been found, in a Viking grave in south Norway. It did not have horns.

At Viking victory celebrations, they drank draughts of their enemies' blood out of drinking vessels fashioned from human skulls. The toast "Skol!" may be derived from this custom. (source)

In Iceland, the Vikings developed a code of laws, a version of a Parliament, and a court that had the power to pass judgement and legislate laws. (source)

The world's oldest parliament is in Iceland, which first met in the year 930 when Viking chieftains met, outdoors, to argue their differences. (source)

The Bluetooth technology is named after a tenth-century king of Denmark and Norway, Harald Bluetooth. Harald was known for uniting various warring tribes in Denmark and Norway, as the technology is intended to unite various other technologies.

The kingdom that the Vikings founded on the Isle of Man lasted until the early fifteenth century, when the island voluntarily submitted to King Henry IV of England. (source)

On November 8, 1898, Olof Ohmann found a slab of rock weighing 202 pounds entwined in the roots of a 40-year-old poplar while clearing a field in Kensington, Minnesota. While controversy exists about the authenticity of the stone, it appears to contain a runic text, written in authentic 14th-century Swedish, describing an expedition of Gotlanders and Norseman to this part of North America. (source)

The Vikings had a god of snowshoes, named Ull. (source)

Viking graves have turned up artifacts from as far away as North America and India, demonstrating the extent of their trading networks.

A Viking longboat would require around 80 oak trees to build.