caldera lake ulmener maar in germany, youngest maar of the region

youngest wilderness wetland water volcanic visible vibrant ulmener tree tranquil tarn surrounded structures sloping sky significance setting serene rural river residential reservoir renowned region reflects reflection pond plant picturesque nature natural mountain meadow maar lush location left landscape lakes lake greenery green germany geological gently forests forest foliage fjord eifel deep clear characteristic caldera blue beauty volcano vulcanic remote calm quiet leisure idyllic ulmen young