The ice cave node is walled in behind a stone pillar and guarded by the yeti. It is the one node with a door you have to earn.
Where it is
The Dreaded Caves of Ice. The marked map is on the location page: The Dreaded Caves of Ice.
Getting it
Kill the yeti. While it lives the node refuses you outright — you are told to slay the beast first. When the yeti dies the pillar over the node alcove rises, and it only stays up for a moment before it starts back down. Once it is shut again anyone still standing in the alcove is teleported out of the room, so meld and get clear. One catch: if the Xeochicatl are the ones who killed the yeti during a node attack, the pillar does not open at all.
Melding
Stand within three squares of the node and use it. The bond raises your maximum mana by three points plus one for every ten points of Mysticism above five, so between three and eight depending on how mystical you are. You can bond with each node once, and the game will list the ones you hold if you ask.
This node can be drained by the Xeochicatl. See Nodes for what happens when one is attacked.