It is at X-11 Y-84 in the Asteroid Belt.
You can only go there after you have defeated all three of the planets (Jungle, Fire, and Ice) and have all three Space Knights with you, so that you can open the portal behind the Golden Key.
The Castle of ArturusThe castle is just to the right of Main StreetThe Castle of the Binary BardThe portal is on a large asteroid near X-11 Y-84 in the Asteroid Belt. To reach the castle, you will need all three knights so that you can use the Golden Key.
The royal castle of the Kingdom of Arturus is just to the right of the Main Street on Astro Knights island. (there is an intervening ad space) The castle of the Binary Bard is located on a giant asteroid in the asteroid belt (X-11 Y-82). You cannot go there until you have beaten all three planets in the solar system (Fire, Ice, and Jungle).
The Binary Bard's castle is on a large planetoid in the asteroid belt, near the coordinates X-11 Y-84. (The asteroids can damage your ship unless you dodge or shoot them.)
It is on tp of the castle roof in astro knight island
The portal to the castle where the Princess is held is on a planetoid in the asteroid belt, near X-11 Y-84.
Mordered is on the secret crystal island that you can access in the asteroid belt once you have gotten all the knights. Be careful he is the princess waiting outside the castle so don't click on him.
The castle is the second area on the island, to the right of the Village.
Once you have built a new spaceship on Astro Knights Island, it will park on top of the castle whenever you leave the island.
Walk to the right.
its on top of the castle
if you mean the planet in the asteroid belt then it is X:11 Y:82
There is no jail on Astro Knights Island. There is a castle dungeon, where an attacking alien robot is being held after his capture. (see the related question)