Those look like Those island caves in Italy. The tide changes during the day sealing the cave after sunset. Quite dangerous if you enter at noon because you might not be able to get out. Some places inside have a roof tall enough to wait but if you don't reach them because of the currents you might drown and get lacerated by the spiky low roof zones.
It doesn't. The price of something affects also similar products. If McDonald's makes burgers 2 dollars more expensive burgerking will do the same the next day.
