If you find Teresa Wentzler's larger pieces a bit intimidating or think they might be too time consuming, I highly recommend these Celtic Knotwork Bookmarks. They require lots of 3/4 stitches and plenty of thread blending, which will give you a feel for what it's like to tackle one of Wentzler's larger designs.
I saw a set of these stitched and displayed at an art show during V-Con, Vancouver's science fiction and fantasy convention, many years ago and have been interested in making them ever since. I'm going to put together a couple more soon, but I started with this design because it has always been my favourite. The other celtic knotwork bookmarks I make will likely turn into gifts for friends and family. This one I'm keeping for myself.
This was stitched on some 32 count cream belfast linen that I had left over from the Octavio Ocampo pictures I stitched. I'm not sure exactly how long I worked on the bookmark, but I'd say it was about 2 weeks of stitching fairly regularly for a couple hours a day.
The Celtic Knotwork pattern is out of print now, but you can get it as a download from PatternsOnline. I'm still disappointed that PatternsOnline's downloads are only available to PC users. Hopefully if you're an avid Mac users you at least know someone with a PC who can download and print patterns for you, even if they don't understand your obsession with cross stitching.
As always the lighting in our house makes it hard to take pictures that capture the true colours of the piece. I would say these last three close up shots most accurately depict the colours, although they are a touch yellower than the actual piece.