Conjuration is probably the most dangerous branch of Wizardry. Well, the most dangerous allowed branch. One rends the veil between worlds at one's own risk.
But wizards have been doing it for a long time. Why, you might well ask, don't they know more about it now? Why is it not a simple matter for a powerful wizard to visit another plane, like another country? There are infinite planes, it's said, if you count the Far Realms at least. It stands to reason that some of them are better than here. It stands to reason that some of them have the answers to any problem you might have.
Most of them, predictably, are very dangerous. You'd send in a team of adventurers first, and you'd make the funeral arrangements in advance.
But somewhere out there -