This place is a maze, so be prepared to spend some time figuring out how to get around. I found Far Sight very helpful in here, as it allows me to see the entire map. Normally all you can see are the pathways, which is kind of difficult to make your way around sometimes.
Upon first entering you'll see Esselarea standing near the entrance. She wants you to rid her grove of an ogre that has taken it over. Agree to help her, then head slightly northeast to the portal.
When you first get through the portal the only pathway leads straight north. In the first clearing you'll see a Gremlin standing there. He'll offer to help you if you can answer his riddle. The answer to his riddle is a rose. He'll then direct you to a certain pathway.
This is a good time to mention that if you wander around a bit you'll come across a couple clearings containing some Spore Beasts, Worgs and Serpents, and there's also a few Serpents slithering around on their own.
Use the map at the top of the page to make your way to the second gremlin. This one is very difficult to talk to, as he only talks in numbers. First say hi, and from then on you'll be given numbers as your options for how to reply. The first answer is 1234.3456. The second answer is 4567., the third answer is 7890., the fourth answer is 5678. After this you can either say 2345 and then click the done button, or just click the done button. Saying anything else will just offend the gremlin.
Find your way up the northwest corner of the grove now, and you'll find yourself standing at the entrance to a clearing with some plain green bushes, and some bushes with red on them. Don't step on any of the bushes with red on them, as this will send you back to the entrance of the clearing. Make your way to the southeast corner of the clearing, and go down the pathway and talk to the third gremlin. He'll direct you straight north to pick some of the pods off one of the red bushes. I've never done this before fighting the ogre, so I'm not sure what it does if you have them.
Once you're ready, go down the other southern passage from the clearing to fight the ogre. He'll drop a Shielding Charm when you kill him, and next to him is the bottle of Xian Ale. Around the corner to the southeast is a little stash of treasure that you can take, including some Bolts of Life and a Heroic Brew.
Make sure that you get everything you want from the Grove before going back through the portal, because one you go through you won't be able to enter the Grove again.