if no-one claims the mountain, is the lake still played?
In the event that the mountain is not claimed, then no, the lake would not be played. However, the likelihood of this happening is not very high since the option moves on to the other players if one is unable to deploy a follower to the mountain.
If you don't mind, would you include a brief description for me again?
This one is a bit more complicated, but I will certainly give it a try. There's 3 new elements... a tile featuring a map icon, the ability to deploy an Explorer, and the discovery of a new, uninhabited area (the tile pictured above).
First, the map icon. When a tile featuring the map icon is drawn, it "reveals what lies ahead". Depending on the number of players, anywhere between 8-12 tiles are drawn from the draw pile and placed face up. These will be the next tiles used by all players. Players will have to choose from these tiles until they are used up.
Moving on, deploying an Explorer. Each player can deploy one Explorer during the game. This will allow players to place a tile that is only attached to another tile diagonally. As long as this tile is disconnected from the rest of the board, only that player may expand the area and earn points in the area.
Finally, when a player draws the mountain tile, they may deploy a Discoverer. That player may lay the new world tile pictured above. This tile does not need to be attached to the placed tiles in any manner at all. However, it cannot exceed a distance of 5 tile lengths. That player will own this new area. Any tile added to the new area by another player earns the discoverer 2 points. This continues until the new world is connected to the original playing area.
That's basically the gist of things. Haha, I told you it was a bit more complicated! You probably didn't expect a novel. Once again, I hope that made some bit of sense!