@JeremyECrawford Can you hide from a creature with blindsight: behind a pillar? In a barrel? Around a corner? Behind a wall? Camouflaged?
— Poljack (@Poljack) June 17, 2016
You can't hide from a creature if you're in its blindsight radius, unless magic cloaks your presence entirely. #DnD https://t.co/9lEjumLFYt
— Jeremy Crawford (@JeremyECrawford) July 14, 2016
Was this intended to imply that blindsight sees through walls?
“A creature with blindsight can perceive its surroundings without relying on sight, within a specific radius. Creatures without eyes, such as oozes, and creatures with echolocation or heightened senses, such as bats and true dragons, have this sense.”
Seems pretty clear that, yes – you can “see” through walls.
Consider the whole “hiding behind a pillar” thing. As long as light from the hiding creature can reach your eyes, you can see them. So if the walls of the room you are in are mirrors, you can see the person in those mirrors because the light reaches you from an angle that is not blocked by a pillar. Similarly, if the pillar itself is transparent or transclucent, and the light can just pass through it naturally, obviously you can see it even if not quite “directly”.
The same principles apply with “echolocation or heightened senses”.
If a creature “sees” using sound, those sounds can bounce off the walls / floor / etc in exactly the same way that light reflects off a mirror. And a pillar can easily be “transparent” to sound waves in the same way glass is transparent to light – the sound travels through the object (usually with some distortion) but continues out the other side and can be detected.
If a creature “sees” using smell, it doesn’t matter if you stand behind a pillar, your scent is going to “spread around corners” because it is in the air itself. A creature with a scent based blindsense with a range of 10 feet can’t smell you properly until you are within that range, but then it “sees” you perfectly clearly, even if you are hiding behind a pillar.
Obviously, there are situations where the DM might argue that you ARE allowed to hide, because you are using different methods to achieve hiding. If a creature with scent based blindsense is stalking you, and you slather yourself in pungent swamp mud to camouflage your scent and make yourself smell like just another part of the terrain, that is the same thing as if you painted yourself with visual camouflage to help blend into the background.
Similarly, if you’re facing a foe with echolocation, and you can do something like silence yourself magically or rely on some loud ambient noise to “cover up” or “drown out” your own sounds, then you can hide “under” that other noise the same way a person might hide under a blanket. Leaping into a pool of water with a roaring waterfall crashing into it will probably make you very hard to detect.