bitcoind - rpc

I'm playing around with a sync'd bitcoind node running locally.

I thought I would be able to perform blockchain-explorer-like lookups on addresses/tx, but every time I try bitcoind tells me that "No wallet is loaded."

If I load a dummy/empty wallet, can I query addr/tx from any wallet, or will it only work for those belonging to the loaded wallet?

If relevant, I'm doing stuff like this:

{ "jsonrpc": "1.0", "id": "explorer", "method": "getreceivedbyaddress", "params": [address] } 

If bitcoind will only give information about the wallet you have loaded, how do blockchain explorers get their information? are they directly parsing & querying the raw data inside of the blocks directory?

Thank you for any info or pointers.