In the middle of Lake Mithrim there is an island.
There wasn't an island before, so the lake is a little deeper than before, creeps a few inches up the shore. There is a splashing noise.
The island is cut off in sharp cliffs around the edges, rising a foot or two over the waterline at the lowest points. On it is an expansive house, several stories tall, with an un-Elven aesthetic and un-Arda implied tech background. Sharp eyes might see non-Elven people, through the windows.