Which ones do you need help with?
WII CYCLING ADVANCED SPOILER ALERT:
Here's the way I get the ones on the beach.
Go onto the beach with the grey house/hotel on your left. There is a flag ahead and slightly to the left. After you have tagged this, cycle on towards the stone arch and you will find the next flag. Continue on towards the end of the beach, as there is a flag behind the smaller grassed mound which I think is the second mound from the end. This is a long way out almost at the end of the peninsula.
I am doing this from memory, but will do an expert level again to see if I have them all.
If you are having trouble finding the one in the dry lake bed (looks like a beach by the volcano when you look from overhead), it's actually a really easy one once you know to look for the cave. It looks as if it is accessed from the paved road, but it's not.
When you have gone across the two rope bridges and down onto the grass below, you will find a flag on the grass. Instead of tagging that flag, look left immediately and you will see a cave with a red & yellow ramp in front. There are usually mii running in and out the cave. Cycle in to the end (the dry lake) and you will see a flag there. It also has a balloon in it when you start doing the freecycling. Once you have got the flag you have to retrace your steps cycling out of the cave and back onto the grass over the ramp and tag the flag you saw before you when into the cave.
Sometimes I do the beach flags at this point, but sometimes I go down and left through the concrete tunnel and do the paved road, turning right for the temple ruins. The entrance to get to the temple is on the grassed area immediately after the little stone path that runs alongside the paved road (there was a flag on this stone path in the beginner cycling). Turn right up the grass, then follow the wide path which gradually narrows and eventually takes you up a stone ramp to the temple ruins. There is a flag here. You'll need to retrace your steps back to the paved road and then follow it to find the ones amongst the windmills and right at the end of the point behind the lighthouse. Then there is a flag in the town and you either go over the red iron bridge, and do the ones on the beach, and then, assuming you have 20 flags, come back towards the starting point and either go back across iron bridge and up the path or go up on the grass and use the big blue ramp and go across the river. Note: You need some speed to cross the river without falling in.
BTW, when you get onto the freecycling which is the one I've been doing lately, there is a balloon on top of one of the grassy mounds on the beach. It's the one with one sided blue ramp to the left of it. You need to go up the ramp to get onto the mound.
I presume you found the ones in the caves (one behind the waterfall) which takes you to the fairytale looking castle and the loop road behind it. The cave to the left of the waterfall cave (as you face it) is the one that eventually leads to the rope bridges.
Hope that helps. If not, let me know where you are having the problems.
8pm. Just done the course again, and I got all the 20 flags and the directions where correct. You can do this in just under 13km to about 13.3km depending on how many corners you cut across the grass etc, and assuming you don't fall into the water or over a cliff.