I was thinking a wooded clearing with a hollow tree where the medics will sit, and three big jutting out branches that will be where the leaders sit, while the deputies and such will sit in the center where all the branches jut out. There could be an almost ring like formation of mushrooms ( fairy ring mushrooms ) where each clan sits. In addition to this, there is a sort of more... mysterious vibe because somehow, the mushrooms that grow on the main tree ( jack o' lantern mushrooms ) light up when it's night time, as if a sign from starclan that hope is not lost. Besides that, there could also be an owl who lives nearby, and seems to hoot whenever the clouds pass over the moon, signaling either the end of the gathering or the angering of starclan. The only way to get to this clearing is by going through a glowing tunnel filled with slightly bioluminescent lichen that flickers and casts shadows over the stalactites that hang overhead... hmm... I wonder what would happen if those stalactites fell... Also there are stepping stones that are surrounded by deep dark water that is too cold and deep for even the urchinclan cats to swim through, so the only way across is by using the stepping stones, signifying unity among the clans because they all have to get to the gatheringplace the same way.