The lounge you will be directed to, and most likely want to use, is the Koru Club (Air New Zealand's) lounge. Some have reported getting into the Singapore Airlines lounge using their *G credentials but I have never had success.

The Koru club is nicer than UA's domestic lounges but not as nic,, IMO< as some other airlines' clubs (LH's Senators for example). They do have hot food, a good bar, showers, and free wifi. It seems to get somewhat crowded in the afternoon.