In the deathly hallows part 1 ds chapter 2 forest of dean lake there is..

There is devils snare that you have to get ride of that on the lower part to the left after you go down the little hill where you started so remove that using lumos and theres a little shopping cart thing you use wingardium leviosa to move it then you put the chest into the cart. That cause the ice to go down. When there go down to the left and on the first platform theres a mermaid creature (sorry I forget what they are called) you move the sword looking like thing (the umbrella) by pressing "a" when it says so then move under it and use lumos again to remove the devil snare. It reveals food for the fire crab. Hit it twice. It will then make the fire crab eat away all the ice. After that swim over the crab (I would try to remember to go over the bubbles to refil your breath at this part. After you swim where the crab is sleeping there are bubbles there. So once that is done use lumos to remove the devil snare away from the sword. Then follow the coins up that appear above the sword and stand on top of the orange box and use reducto (I think thats what it is called) to remove the lock then two barrels will fall out. Use reducto again on the barels that fell and with reveal a ice pick and hammer. Use wingardium leveosa (excuse my spelling) and it will release the sword. Pick it up and it brings you to the next level. Sorry for the long winded responce but I hope this helps