The Anvil is the largest cloud in Nimbus Ascent, a huge thunderhead with a flattened top, hence the name “anvil”. It is bits of white colored in some places by storm cloud grey, with occasional flashes of magical energy bursting from within, lighting it with flashes of lightning.
The Anvil is the only cloud so large that it spans all the layers of the skylands. A truly massive living ecosystem of its own. Other clouds in Nimbus Ascent will be tall, but only The Anvil spans all the layers, a good half again as high as the next highest mountain/cloud. The Anvil has a special place in the spirituality of all the people in the Cloudlands.
The Anvil is host to a particularly rich ecosystem (somewhat like that of a coral reef). Large numbers of epiphytic plants grow on it, using its body for support and drawing nutrients from the air. Many small animals use it for shelter or eat its fruits and seeds, or feed on other small animals. Hail Elementals protect the Anvil from any who would seek to harm or colonize it, forming a sort of immune system for the Anvil.
There is some debate over the exact nature of the Anvil, whether it is one single massive organism, a particularly large clonal colony (like aspen trees), or many plants working together in concert.
It is rumored that if one could reach the top of the Anvil, great magic is located there. However the air up there is so thin that one couldn’t fly, and climbing would mean dealing with swarms of Hail Elementals.