Okay, Paul....here's my take on your dream, for whatever it's worth. ;-)

Your dream, I think, is primarily about going down into the deeper levels of your subconscious mind and visiting old thoughts and emotional impressions that are stored there. Those memories can be from any point in this life, even pre-natal...and some think they can also be from your past life experiences, though I doubt that you'd go for that concept.

In any case...

"I was at a bus stop in heavy rain"

The "heavy rain" is your emotions...the flow of emotion.

"Some friends were with me"

The "friends" are your most familiar thoughts, habits, and emotions...those you are presently most comfortable with.

"There was a warehouse nearby, a big antiques emporium, and we decided to go inside."

That is the warehouse of all your past memories, thoughts, and emotions, all of which are stored in your subconcious mind. You and your presently familiar mindset went in to take a look through the subconscious warehouse of your mind...your own past, much of which you do not remember consciously.

You encountered various past memories, thoughts, and emotions, all symbolized as some antique object or another. I won't bother dealing with those in any detail. These symbols are quite hard to interpret anyway, and it would be a lengthy enquiry.

You then went down a stairway to another section. When you go down in a dream, you're usually simply going deeper into your own subconscious. You're going to a deeper (more hidden) level of your past.

The "hippy-style" people could symbolize a part of your life in the late 60s/early 70s...your mindset at that time.

You then went down a sharp slope...even deeper into your subconsious memories of the past. The security guards who stopped you there were some part of your own mind that wanted to protect you from being exposed to some sort of past memory that you would probably be better off not to consciously confront at present...or else they are your own fear of confronting it. Therefore they wouldn't let you through that door.

The whole dream, I believe, was about you. That's what our dreams usually are about...they're about dealing with our own inner self and resolving various emotional issues.

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And that's simply the best interpretation I can give of it. I'm not saying it has to be that way. Just my own take on it, and that's all.