walking or driving? downtown Honolulu is about 15 minutes from waikiki beach. If i remember correctly. It's really close. I think waikiki is a community in Honolulu
Honolulu is located on the island of Oahu. Kauai is another island.
Flight time from Honolulu to Lihue (on Kauai) is about 37 to 45 minutes, depending on the winds.