Hi There, Any advice for a beach to strech my legs on during an 8 hour layover in Nadi or anything else fun and easily accesible in Nadi?
Thanks

You could, at a stretch head to the Coral Coast (90km away), but Id head to Denerau and get day use (pre-book) of one of the 5 star hotels for pool, change rooms etc. This would also leave some time to visit Nadi for shopping if you really wanted, but the shops at Port Denerau have some reasonable stuff, thus much easier.
Depends on what experience you want......
If you are wanting to relax and enjoy your several hours,,, then yes,,, absolutely head to Denerau and find a bar and pool you like and relax,,, grab a massage and then wander the Port Denerau Marina shops...
If you are wanting to experience some Fijian culture then pay what ever the going rate is and hire a taxi to take you to Coral Coast.... or better and cheaper still,,, hire a car for the day and head that way,,,, (when you exit the airport,, turn right and stay on that road,,, it will lead you to Sigatoka which is the town servicing the coral coast)..... lots to see,,,do some google searchs and narrow it down to your personal taste.
Enjoy

Highly recommend a day room at one of the airport/Martintar hotels with a pool. Get off the plane, come out and get transfered immediately. Have a good breakfast, shower and dip in the pool. Quick lunch and back out... Loads to choose from, some FULL of kids so be careful if this is an issue (Tokatoka, Raffles Gateway...)
If you stay in the airport, it ain't so bad if you're a hardy traveller. AFL have fitted Pacific Green couches which are very comfy. For coffees, bagels and stuff head to the ROC cafe near departures. (the other outlets' coffee is awful!).