Wallswim 1:
(see top-left. The screen above has non-solid tiles)
Wallswim 2 - x981y992:
(high jump needed to reach)
I only found the secret area thanks to pfrangip's mention of radio. I did go back to x1018y1068 on my own, but didn't find the ghost blocks screen to the right of it. I always tried jumping up, not to the right.
I slightly cheated in the secret area: cheat-saved at x1209y1064 to bypass the tedious non-challenge. There should have been a save point.
Oh, and the radio was nice.