Besides a pool, what did Hezekiah make to bring water into Jerusalem?

Answer: A tunnel

2 Kings records how Hezekiah made the pool and the tunnel (KJV: conduit) to bring water into the city.

“As for the rest of the acts of Hezekiah, along with all his might and how he constructed the pool and the tunnel to bring water into the city, are they not written in the Book of the Chronicles of the Kings of Judah?”— 2 Kings 20:20 (BSB)