The key is stuck down a drain behind the kitchen in the castle. Go get a bucket or jug and fill it with water at any water source and the sink in the kitchen gives you water (if you did not bring a bucket, up the stairs there is a rooms at the corner and you can get a bucket in there). Use the bucket of water on the drain and the key will be washed into the sewers. Enter the Varrock sewers using the manhole located immediately east of the castle's keep. Follow the north-western path until you get to a stream and go to the small corner. Search for a rusty key on the ground; it will not appear on the minimap. Grab it.
Assuming that you used the bucket of water with the drain, the key should be here in the mud http://img502.imageshack.us/img502/6241/varrocksewers.jpg
bucket of water
It is just outside the inner castle wall, by the kitchen. The kitchen is in the north-eastern portion of the castle.
just head down, into the sewer, now just follow the hallway north. Go to your left, and you will see a little glint where the key is, if you already don't see it.
If you're talking about during the quest Demon Slayer, then what you do is use a bucket full of water with the drain, causing the key to dislodge and go into the sewers. Then go near the Church, and there should be a manhole. go down into the sewers, there should be two hallways. go through the hallway to the left, then turn left when you get to the water, and behind a broken wall, with (i believe) skulls piled up, there the key will be :) hope that helps!!!
Assuming that you used the bucket of water with the drain, the key should be here in the mud http://img502.imageshack.us/img502/6241/varrocksewers.jpg
bucket of water
It's Varrock Castle. To get it you need to get a bucket of water and use the bucket of water on the kitchen drain. Thie key will fall into the sewer, you'll need to go to the Varrock Sewers to pick up the key. The key will be on top of a pile of mud near a clump of several skeletons.
get a bucket of water pour it down the drain and get it in the sewer go to runehq.com or runescape.wikia.com for quest guides
in the drain in varrock place us water in the drainage pipe and then go to the swears to wear the pipe ends
It is just outside the inner castle wall, by the kitchen. The kitchen is in the north-eastern portion of the castle.
just head down, into the sewer, now just follow the hallway north. Go to your left, and you will see a little glint where the key is, if you already don't see it.
you can find the key in the drain by the Yews by Varrock Castle. use a bucket of water on the drain, go underground (by Varrock Castle). there are two ways, take the left way and go the first time you can go left, then go left and there is a rusty key. (for extra: the last two keys are upstairs in Varrock Castle and by The wizard Tower. 1. talk to the guy on the 3rd or 2nd floor ( i don't know who and what floor.). make a good story with the guy and he gives you the key. 2. take 25 normal sets of bones to Wizard Tower. talk to Traiborn, ask him to a key that sir Prysin has given him, but he doesn't know what are you talking about. but he remember an another key. he ask you to give him 25 sets of bones. get these sets and give it to him. than he gives you a key, the third key.
sorry you cant make keys on runescape unless of corse it is the crystsal key.
There isn't a key for it unfortunately.
A brass key.
If you're talking about during the quest Demon Slayer, then what you do is use a bucket full of water with the drain, causing the key to dislodge and go into the sewers. Then go near the Church, and there should be a manhole. go down into the sewers, there should be two hallways. go through the hallway to the left, then turn left when you get to the water, and behind a broken wall, with (i believe) skulls piled up, there the key will be :) hope that helps!!!