Get the Secret Message from the maid's room (castle, first floor, left) and see the girl in the hayloft of the mill. She will give you the Cosmic Symbols card. Pressing the three symbols, and the sun, will open the plaque on the fountain in the Main Street square.
The only "card holder" on Poptropica is for the Cosmic Symbols password on Astro Knights island. Th girl with the card is upstairs in the Mill.
you put it into the spaceship ontop of the mill
it is to the right of the castle, just keep going right.
On the water wheel at the mill. (Far right side of the Mill area) You jump up to it
There is no well at the mill. There is, however, a rope, and a secret society member, and a hidden hovercraft.
In the field between the castle and the mill. A farmer will give you a bag.
You can get a bag of manure (but just one) at the farm near the Mill.
The plaque is on the fountain outside. It has various planets, stars, and moons on it. (You will need to take the Secret Message to the upper floor of the mill to get the password symbols.)
The mill is out of commission. The only way to get across the mud swamp is the hovercraft in the mill's attic.
The windmill is at the far right side of the island. There are three areas : the Village, the Castle, and the Mill.
Climb into the loft of the mill and hang on the short rope there.
The marsh is all the way on the right, go right from the Mill.