New answers tagged macro-lenses
If you don't want to carry two lenses, you might want to add an Extension Tube to use with your 18-135 STM: http://www.the-digital-picture.com/Reviews/Canon-EF-S-18-135mm-f-3.5-5.6-IS-STM-Lens-Review.aspx
The Canon EF 24-70mm f/4L IS USM Lens is the closest to what you desire. It isn't a true macro 1:1 lens, but it does provide .70x as well as a fairly close miniumum focusing distance of 7.9"(200mm). The image quality will far exceed the current zoom lens you have, and the macro quality is very high for a zoom or non dedicated macro. It's a great lens ...
Personally, I think you need to bite the bullet and just carry both lenses. Two lenses is not a huge amount of gear, and the 100L Macro is arguably the best macro lens you can get for the Canon mount. You could rent an EF-S 60mm f/2.8 USM Macro for the trip, which is smaller/lighter than the 100L, but it's not going to replace an 18-135 for walkaround use, ...
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