The cave of fear is past the spider statue. you have to clear a stone door. Then you have to clear spider eggs (all of them) in the main quest to unlock the cave. The cave will have spiderwebs on it and eggs by the entrance.
A dig site produces artifacts, which the game will ask for as items you will need to clear quests.

Not sure about the Cave of Fear but the dig sites are in the store for buying.

if you stay on the island group but reload your game it should go back on dry land

It's on a box on the island it should sparkle. The map shows which islands

I finished the boat quest where do I find the magical symbol

What is the boat quest? I need the magic symbol too.

What do you have to do to complete the boat quest?

If it's forgotten shore its in the water. To the south if you find out how to get it. Let me know

sometime the crate the holds the map pieces can be found behind trees etc. sometimes you have to visit a couple of times before it shows up. but you can try this, do not come out of your island but reload your game. sometimes it will show up then

if you click on the map (first icon bottom left hand side) it takes you to your islands, map pieces pop up from time to time. you just click on the map icon next to the island.

Make sure you have shovels when you visit other players' islands. There will be sparkling chests on the shore that you can open with one shovel each. You can get stars, coins, etc. But if a player hasn't played in a while, there will be no chests to open.

no when you visit you do not receive items from them. people who you are 'friends' with who play the game can gift you items when the characters have food icons above their heads this is when they can send. they can not however choose what to send

also you only need to revisit them when there is a map symbol next to that island. this indicates that you can collect another map piece from this island

the wooden doors take 5 food cans

which cave are you stuck on?