Is it legal to explore abandoned buildings?

If no one owns it, is it OK to enter?
If no one owns it, is it OK to enter?

Exploration of the physical world takes many forms. People trek into the wilderness, climb mountains, climb trees. Archaeologists dig. Spelunkers crawl. And urban explorers sneak into storm drains, tunnels and old abandoned buildings left to rot (or so it seems).

The urge to engage with the past, especially the forgotten past, is nothing new. Neither is sneaking into vacant buildings -- especially scary or unique ones, and especially if something terrible or beautiful or simply utterly human happened there. Exploring the less-traveled, boarded-up urban world is not so different from exploring the open, natural one, except that it's likely to be illegal.

The issue with this type of urban-exploration activity is trespassing -- at its most basic, being on someone else's property when you're not supposed to be. In some cases, trespassing is easy to identify: If you walk into someone else's home after the owner told you not to, you've met the requirements. In other cases, though, it can get foggy, and this is one of those times. For instance, if a building is abandoned, there's no owner to refuse admission ... right?

Not necessarily. And even in that case, trespassing might still apply.

Say you're looking at an early 1900s warehouse, vacant, graffitied and unsecured. You have no intention of stealing or vandalizing. You just want to go in, maybe stay a while.

Can you, legally?