If you happen to be in the desert and you see this weird portal shit, do not go near it.  You will fall into a desert dungeon and get your ass beat fairly quick.  You will die almost immediately.    Then your limp body will be transported to the nearest safe spot which will be a far ass way from your horse.  You’ll have to run back to get your horse or find the nearest city where there is a stable to remotely collect it.  If you think you are strong enough to handle demonic beasts and you don’t care if you die in the most brutal way possible or that you have to search the desert for your damn horse, then by all means, fall down the hole.