Over parts of Wales, you wouldn't want to practice one below 5,000 ft: Chances are you don't have a whole heck of a lot of terrain clearance and you are likely to be in cloud.
I have been through severe icing at 5,0 in June up there and had to climb out of it.
I disagree with previous - at 500' you know whether or not you're going to hit the spot.
What would you do if you went to < 200' and applied power for the go-around and the engine did not respond.
That's more like cardiovascular exercise!
I see no point in setting aside an area to practice in - the real thing ain't going to catch you out in friendly territory. I recall a previous about flying tight circuits just in case of engine failure - so you just arrived near the field after a two hour leg, gee, better fly a tight circuit cause I'll be in real troble if the engine quits now...