Johnny: Yes. Nama gotta (or memory records) can be accessed by either punna iddhi or by cultivating jhana.
Recalling previous lives by punna iddhi means, due to a past kamma they are able to recall. Children recalling past lives can be thought to fall under that too. Some others can recall memories in this life in great detail: “Recent Evidence for Unbroken Memory Records (HSAM)”
Those who cultivate the fourth jhana may be able to recall many past lives. Even before the Buddha, there were yogis who could recall many past lives. But those are mainly past human lives.
– A few are able to recall many, many past lives including those in different bhava. A Buddha can recall as many of those at a great speed.
Tobias asked: “Are stupas closed chambers so that no human can go inside?”
Yes. A stupa is a huge structure. Dhatu are stored in a small chamber inside. But it is fully closed. No human can go inside. The following are pictures of Stupas:
“Pictures of Stupa.”