The goal of the game is to retrieve the Deeplight Stone; to reach it, you have to collect four runes, as well as a number of keys to open doors that block the way. You don't need to collect all the keys or explore the whole place to finish the game, but there are achievements for doing that. The ruins are a maze with traps, but no puzzle elements; there are teleporters to get around the place faster once you activate them.
In short, explore the ruins to get the four runes that unlock the way to the Deeplight Stone; you also need to find keys, hidden in hard to reach places, to unlock doors that seal certain areas. Entering a room automatically saves your progress.