re: What do you do with 100 grand for 1 year if

The answer is not so easy and depends on assumptions. Considering today's markets, you'd be much better off paying off that 6% loan. However..

1) You lose liquidity, should an emergency arise.
2) If rates go up to 13% in 10 years and you need to borrow money against your home, you're going to have to pay that rate. It'll make that 6% mortgage seem like a gift. If you had money invested, you would be EARNING at that higher rate during that time while paying the 6% mortgage and if needed could cash out the equity invested instead of taking out a loan.

You could look at ATOIX, tax free current yield of 3.66%, the NAV has been pretty stable:
ATOIX chart

If you look at the scaling it has only fluctuated nominally, like in a range of 10 cents the past two years. Read the Alpine prospectus and SAI. YMMV. I own that and Vanguard's limited term tax exempt, which is much more volatile for a relatively short duration TE fund, but I bought most of it Nov/Dec last year.

Ally Bank has some higher yielding CD's with no early withdrawal fees, but nothing to write home about after tax. Or CapOne has a Costco branded online savings account paying 1.85% if you are a member. Hard to make any money in fixed income products these days.

You're welcome, you might want to check local credit unions or PenFed.org online. PenFed has some good deals from time to time, but are better suited for someone who knows with certainty they will not break a CD as the penalty ranges up to 60 days interest. Some have said Alliant CU online has good deals, but I could not find a way to qualify for membership, you may be able to qualify.