Similar to ridge lift is a phenomenon called "wave lift". This is a little harder to imagine. It arises from the wind blowing against a hill again, but this time the air comes back down (on the far side of the hill) and "bounces" off the ground and goes back up again creating a very smooth upwards flow of air. Often, this form of lift is capped by a cigar shaped "lenticular" cloud.
This wave may go back down and up again for several cycles, meaning that you don't actually have to be close to any hills to use it! The longest ever flights in gliders have been done using this lift - the world record is just over 3000km. This was done along the Andes, all in one flight and one day. Here in the UK, flights of over 1100km have been achieved, this time using Scottish wave. Wave lift is also known to go very high - the world height record in a glider is just a little over 50,000 feet!