From the top right platform, jump to the left into the thorns, then climb the left wall.

Requires:

{
  "thornHits": 1
}
{
  "or": [
    "canUseIFrames",
    {
      "thornHits": 1
    }
  ]
}
"canWalljump"
{
  "not": "f_DefeatedPhantoon"
}
{
  "or": [
    "canRiskPermanentLossOfAccess",
    "canCarefulJump",
    "Gravity"
  ]
}

Dev note: The canCarefulJump and Gravity are here, as with either of those, there is access across with or without f_DefeatedPhantoon.