The Cosmic Symbols password card lets you enter the room under the fountain in the village. Pressing the three symbols (and the sun) on the fountain plaque will open the secret door.
One of the farmers gives you some manure.
put the manure that i dude gives you in it.
Sir peleas gives it to you at the bottom of the volcano cave. (see related question)
The missing page is under his bed at the museum, and gives the coordinates for the Pewter Moon. The rest is just the island storyline.
The wall is only loose dirt. Keep pushing until it gives way.
If you mean the ones that the Queen gives you from Astro-Knights they are the planets at which the three knights are at.
You use the manure that the man gives you
There are 3 space knights, one on each planet on the card that the queen gives you. Travel to each of the three planets, and the knights will help you or give you the weapons you need. (On the jungle planet, you have to find the Laser Lance on your own, down in the forest of metal flowers.)
Mordred's journal is in the castle library, but it is missing a page, the one that gives the coordinates (X-56 Y-52) to the nearby moon.
The Queen gives you the coordinates for the planets where the three space knights have gone, but for the saucer Excalibur they are too far away. The nearby moon at X-56 Y-52 is noted on the page from Mordred's journal (under his bed).
The queen gives you the list of planets that the knights have gone to. But your fuel supply won't reach them. (You go to the moon at X-56 Y-52. The coordinates are on the missing journal page - see related question)
The queen gives you a card with the coordinates of three planets, which are too far away for the saucer Excalibur to reach. The nearby Pewter Moon is at X-56 Y-52.