The song "Sentinels of Darkness" by Aeternus talks about the beauty and power of nature, particularly in the winter landscape. The lyrics describe gazing at the tranquil, white land and feeling free and surrounded by the spirits of nature. The song also mentions the call of the wise owl, the strength of the wind, and the healing power of nature. The overall theme seems to be about finding peace and strength in the natural world, and the song captures the mystique and power of the winter landscape.