I'm gonna be the first to suggest exploring further, Reka's tomb was hard for me, as well. I missed almost 1/3 of the secrets on the first try. Watch a video walkthrough on YouTube, after you've scoured the area once. That has been my strategy thus far, doing the area alone, then watching others do it, and it has payed dividends.
here are pics showing the two chest key locations in Level 3 Tomb of Reka. The first pic shows the map location, second pic shows the 1st person view! also in this level, there are a couple regular treasure chests that aren't locked that are easy to miss, if you don't explore each room carefully, so watch out for those! at least one, was hidding in shadow in the corner of a room. tricky level.
I am working on making these pics for EVERY chest key in the game. when i am finished i will upload to youtube.
My favorite level thus far.