Rubies are the premium currency in the game. You can use them to finish construction instantly, purchase special buildings, special tools and other items. Many special events do have to do with spending rubies, like special offers or the Gift Peddler. There are also sometimes way to earn rubies in nobility contests. There are a variety of ways for players to acquire rubies - some requiring real world money and some merely taking time. Some players consider rubies to be almost "game breaking" although this is debatable as some players see them as more of a challenge when up against a "ruby player" opponent.
There are a wide variety of ways for players to acquire rubies - the quickest being simply to purchase them with real world money via Goodgame Studios. Other methods include levelling up, by completing certain quests or simply just by logging in once a day. Players can purchase a varying amount of rubies at a variety of prices. The prices range from £0.99 for 1,500 rubies all the way up to £49.99 for 112,000 rubies.
However, in the U.S, prices can range up to $4.99 for 4,700 rubies, all the way up to $99.99 for 130,000 rubies. Seen to the right is a screenshot of the payment shop, depicting the varying prices and quantities of rubies available for purchase. Along with the differing amounts of rubies available for purchase, there is also a wide variety in which players can actually pay for them, inclduing via text.
Yes, such a thing exists. The ruby mine is a small, cone-tipped tower made of stone with a blue cone-shaped top and mine cart tracks running down into a tunnel next to the tower. The ruby mine is a once-in-a-lifetime special offer presented to low level players (below level 25). I have one and I'm level 70. The ruby mine costs 30,000 rubies in a one-time payment, and will give 250 rubies every day for 360 days, totaling 90,000 rubies, which is three times the original price. Of course, subtracting the original 30,000, the profit is 60,000 rubies.