Cape Cod National Seashore was set aside to preserve its natural and cultural resources, with regulations intended to protect those resources and ensure visitor safety. Natural and cultural features are protected by federal law and must not be disturbed, and picking flowers, using metal detectors, and taking, feeding, or harassing wildlife are prohibited. Visitors are to keep trails, roadsides, and other areas clean, while oversand vehicles are limited to designated sand routes by permit and indiscriminate dune-driving is prohibited. Seat belts are required in vehicles, pets must be leashed and controlled, and they are not permitted in public buildings, on lifeguard-protected beaches, or on nature trails. People are to stay on established paths to avoid trampling vegetation and reduce exposure to ticks and poison ivy, remain out of areas closed for wildlife protection, and avoid open fires except where authorized by permit or otherwise allowed in certain picnic areas and on sandy or rocky beaches bordering tidewater. Public nudity is prohibited. Safety precautions warn that poison ivy and ticks are prevalent, sand collapses easily, and ocean waters may contain riptides and underwater obstacles. Visitors are cautioned against too much sun exposure, and glass containers, rafts, rubber tubes, and masks and snorkels are prohibited on lifeguard-protected beaches. On designated bike trails, riders are to wear helmets, with helmets required for riders 12 and younger, ride single file to the right, avoid speeding, and watch for hills, sharp turns, other users, and windblown sand, while summer visitors on narrow roads are warned to be alert for heavy traffic, bicyclists, and pedestrians.