The Cape Cod National Seashore offers two very different guided walks this week. “Sharks and Seals: Cape Cod’s Dynamic Duo” is a one-mile walk on Race Point Beach in Provincetown on Friday, May 21st, from 10 to 11 a.m. Or enjoy a “leisurely stroll” on Nauset Marsh in Eastham on Saturday, May 22nd and Sunday, May 23rd, from 11 a.m. to noon. Registration is free. Call 508-487-1256 for the “Sharks and Seals” walk, 508-255-3421 for the Nauset Marsh walk.