GAZA CITY, Gaza — Underneath the Shujaiya neighborhood in Gaza City, mattresses once used by Hamas fighters remain on the floor of a dormitory built in a tunnel by the militant group. Nearby is a fully tiled bathroom with a toilet and sink that once had running water. Women’s underwear still hang on one of the walls next to one of multiple cables used to power the lights and other electronic goods. The Israeli military says this was one of a honeycomb of tunnels underneath the enclave, all of which will need to be destroyed before reconstruction can begin. NBC News accompanied the Israel Defense Forces into Gaza on Monday, under conditions that prevent the use of images of most military personnel for what the IDF says are operational security reasons. Requests for independent access to Gaza from NBC News and other media organizations have been refused by the IDF.…