In the undergraduate toplogy course we were given examples of spaces that are $T_i$ but not $T_{i+1}$ for $i=0,\ldots,4$. However, no example of a space which is $T_3$ but not $T_{3.5}$ was given. Later I was told by a colleague that such examples are rare and difficult to construct.

I know there is an example of such a space, called the Tychonoff corkscrew (or the spiral staircase), in the "Counterexamples in topology" book by Steen and Seebach. I've also found the following paper, though at the moment I'm not able to view it: A.B. Raha "An example of a regular space that is not completely regular", Proceedings Mathematical Sciences 102 (1992), 49-51.

Are there any other, folklore examples of regular spaces that are not completely regular? Are there any relatively easy ones?