Are the mosques big compounds that are walled?
Some mosques are large and others, particularly neighborhood and private mosques are not.
Some are. Some are more like storefronts. Some are "compounds", but not walled. Others are pretty much fortresses. Walled compounds with many buildings other than the Mosque proper (sort of like the Alamo, which started life as a Spanish Mission) It's like asking if Churches are big ornate buildings with associated gyms, parking garages, etc. etc. Some are, some aren't.