Tunnels is good spot for a guide but if you choose otherwise - get a verbal orientation of the site at least. A couple of the tubes get a little challenging if you get off the normal path. Also - current can rip up there especially in the pm. The entry/exit is the same spot. If the current starts to rip you have to travel a good distance back up current to the exit. Otherwise you have to crawl out over the reef for a long distance to get to shore. Naturally many days are mellow but as always it is good to be cautioned about some of these things.
Koloa is a relatively protected bay and north/south navigation which makes it easy to dive without a guide. Essentially a horse shoe underwater you can use natural navigation pretty easy there. At the same time I have had people for years say there is "not much to see" there. ??????? With a guide you are sure to see Frogfish, lionfish, leaf scorpions, devil scorpions, dragon morays, harlequin shrimp, cleaner shrimp, etc...
Maybe consider a guided dive there then rent the rest of the time? You can blow 4-5 tanks exploring there easily.
Hope this helps a bit.
Water has been awesome. Excited for you!
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