Comment by sp332

Tor hidden servers have changed recently so this may be a bit out of date, but the client (at the Twitter user end) has to choose all the relays between itself and the endpoint. The server (Twitter) is also hidden here, so the client cannot make a path all the way to it, the way it could for a normal website. So Twitter publishes the address of a trusted relay instead. The client makes a path to the relay, and the relay forwards the request on to the hidden server.