Here I will show you how to make a portal that looks dark and hunted and junk like that.
1. Create a New Document. Any size is fine.
2. Set your Background Color to black and your Foreground color to red (I used #CC000)
3. Apply the Difference Clouds Filter, Filter-->Render-->Difference Clouds. Reapply (Ctrl+F) as many times as desired until you get something you like.
4. Then apply the Pinch filter. Filter-->Distort-->Pinch. Make sure you set the amount to -100%. Reapply 3-4 times.
5. Make a perfectly circular selection by holding Shift while you drag the eliptical marquee tool. Make this in the center of the picture.
6. The go to Filter-->Distort-->Spherize and set the amount to 100%
7. Go back to the pinch filter (Filter-->Distort-->Pinch) and set the amount to 100% and reapply until you notice that everything converges in the center of the "hole".
Your done. I'll upload a pic of what it should turn out like soon.
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