Some of them you can walk through but don't go in the middle of those ones unless its the right one and the others will just sink you if you get to close to them.
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you don't "pass" relic castle you go to it later and meet team plasma (you also get a fossil if you talk to the backpacker!)
At one point in the plot, you will be told to go there. Only then will he move and allow you access.
if you go down to the very bottom of the relic castle go up the all the stairs and you should be out. hope this helps! =)
In relic castle
Walk down as far as the backpacker and then walk left one, and then down towards the stairs.