Thieving is a skill that can be trained at Thieve (Falador). It gives you a lot of money and is fairly fast to train. When you get 99 thieving, you can steal from the Silk Stall to get 4m per steal. Although not the fastest skill to train to level 99, it is arguably the fastest to get from level 99 to the maximum of 1,000M exp assuming the most common methods of training are used,