I'm towards the end of the game because I've got all the weapons, I'm now in an underground cave level where it's very dark and you can only see the things around you. There's several different routes to take but all the ones I've tried lead to a dead end. In the middle there is a save game spot and two of those health fountains (the red one and yellow one) there's what looks like train tracks which lead to doors on either side but neither of them open, does anyone know where to go from this point?