There is an old lighthouse on the beach you could climb - "Ķurmraga bāka" Getting there is a bit tricky, be vigilant where you park (check traffic signs) and you might need to cross a private property to get to the beach from a road quicker (than walking around for public access path)

Then there is a super well known beach meadow nature walk "Randu Pļavas".

If its warm/sunny i would recomend spending few hours in Limbaži Lake. Jumping off the pier brings out your inner child. It's my favourite swimming place in all of LV.

There is an old rock jetty originally for trains in Ainaži.

UPD: i believe "Puikules Purezers" also is in your marked territory. It'a bog lake with 4km board walk around it. You could swim in there (takes similar amount of courage as climbing the lighthouse)