Smarter to avoid South of Calle 22
[QUOTE=Jicks;2092423]Looks like Trannies are allowed only at Calle 20 and Carrera 15 within Santa Fe. There are many girls too in both streets but confirm before approaching.[/QUOTE]I've been told several times by locals, better to stay on or to the north of Calle 22. (North is to the right if you are walking from the Transmillenio. The Calle numbers are rising.).
Personally, having walked through the area you mentioned during the day with a local, I highly doubt you will find a gem around Calle 20 that you wouldn't find in the relatively safer area.
By the way, another local told me he was robbed at knifepoint during the day once in Santa Fe. I've never had any problems, but it is better to be aware.