Terra Cave is a cave found by the shore after defeating the Elite 4. It is on Routes 105, 125, 127 or 129. You need to go to the weather center and he'll tell you where it is. However if you take too long finding it, it will move on
It's a basic cave bit first, then the Misty cave
In the Misty Cave, you will see Groudon. Go to him and you battle him. Groudon is at Level 70 so be prepared
Thats all that is in Terra Cave

Terra Cave Picture Locations

Route 114
Route 115
Route 116
Route 118

 
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