String bikinis were ever so popular in the 1970s. My older sister had several sets and I had a few myself. They were great for lounging around in the sun, but terrible if you wanted to actually swim in the water without exposing your bits to the crowd.
The following string bikini pattern was published in The Australian Women’s Weekly on October 30, 1974. The pattern below is not to size. Instead, use it as a basis for creating your own string bikini and, if necessary, use a pair of underwear to help make a better fitting bikini bottom.
If you really want to get your hands on the correctly sized pattern, you may be able to find an original copy of the magazine on either Ebay or Etsy. Sometimes you can buy the magazines in large lots. If you have the money and the space, I’d highly recommend it because the magazines have a lot of great patterns and crafts in them.