Some missing parts and rusty things

I was exploring near the beach in Portugal. Near the sand dunes and beneath the pines there are some mysterious paths. Some of them only take us to the beach, others to some abandoned places that were once used to store things related to agriculture.
In one of those paths I discovered a rusty portal, already with missing parts.

Below is the access door to the location. As you can see it is in poor condition and you can go through it easily.