YES, that's Kastraki It can also be sometimes found under name of ASINE... because the beach is right across from small ruins site of ASINE (famous in the Iliad Era - the King of Asine sent a troop-ship to Troy!). This is a secret-gem discovery of mine... you can get a local bus there from the NAfplio bus station (ask also schedule of return bus). Ask driver to drop you off At Asine crossroads (DO ask where to stand for return bus; you'll have to flag it down). Then walk 200 yards or so down a shady lane and Presto! there's a cove... to the left, a little sandy/pebble beach, next to it, ONE Taverna, up on a hill... and just below taverna, a stony beach (NOTE for trip: Always pack cheap "water shoes" for Greece -- some of finest beaches are stony).
Use Taverna restroom to don swimsuit. There are a half-dozen umbrellas/sunbeds, no charge, but of course u buy a beverage. Afterwards, a nice lunch under shade of taverna canopy. NOTE: from this little cove, you look across to Tolo --- jampacked with tourists, and NO facilities (restrooms/changing rooms) available except at hotels. Meanwhile, Kastraki is serene.
With extra time -- cross road to Asine ruin... there's a big (HEllenic-era) wall-ruin, on other side of it is a big shady CAMPSITE... and beyond it -- Surprise! a long SANDY BEACH, with a dock or 2. There are no amenities (no sunbeds, restroom, cafe etc), just plain beach... also may be some jelly-fish. Good for a short swim diving off a pier there. After my 1st time at Kastraki, 3 yrs later I was with 3 other people at end of a one-day "ruin-a-thon" (Mycenae - Tiryns - Epidaurus). We were wearily driving back, when I recognized the bend in the road & screeched STOP! We all had swimsuits with us (Be Prepared) so had a lifesaving swim, then stayed at taverna (owned & run by a lovely young family) for delicious sundown fish dinner. Perfect ending to a long day.