Kami ay naglakad-lakad sa tabi ng baybayin.

English Translation

We went for a walk along the coast.

Naglakad-lakad kaming sa tabi ng baybayin.

Naglakad-lakad kaming kami sa tabi ng baybayin. (“Sa tabi ng baybayin” describes the walk—not the narrators—so using -ng to link this to “kami” makes no sense. Also, just as a general grammar point, I’m at least 99.5% sure that it’s ALWAYS wrong to use a “na”/"-ng" linker in front of “sa + NOUN”.)