"An underground terrorist city"

Via Powerline, we find where the concrete went - tunnels into Israel for potential attacks in September.
Israel has reportedly discovered at least 30 tunnels, and has destroyed several of them by employing bulldozers. IDF excavation of the tunnels has resulted in the seizure of tons of Hamas supplies, as well as the discovery of plans for future operations. Clearly, the network of tunnels -- using hundreds of tons of concrete that might otherwise have been used by the Palestinians for building homes, shopping malls, parks, schools, hospitals and libraries -- indicates that Hamas had been preparing for an ongoing conflict for at least a year. According to the reports, each tunnel has arteries, veins, offshoots, and offshoots of the offshoots in intricate and complex arrangements.