How to find Thurmont, Maryland:
Coming from Washington, DC - Richmond, VA - or anywhere from the southern cost States:
Follow I-270 to Frederick, from there, I-15 north (direction Gettysburg, Pennsylvania). Thurmont is about 25 km (15 miles) from Frederick (half way to Gettysburg).
You should count about 1-1.5 hours driving time from Washington, DC.
Coming from Philadelphia, PA - New York, NY - Boston, MA - or anywhere from the Marytime States and Provinces:
Follow The Pennsylvania Turnpike (322) from Philadelphia to Harrisburg. From there, turn south onto I-15, go past Gettysburg toward Frederick, Maryland. Thurmont is about 10 km (7 miles) after the state border. If you come to Frederick, you will have to make a U-turn...
You should count 3-4 hours driving time from Phildelphia.
Coming from Buffalo, NY - Toronto, ON - Montreal, QC:
There are many possible routes to Harrisburg, but the simplest is to hit I-15 that starts south from Rochester and goes all the way..... From Ontario and Buffalo, the fastest is probably The New York State Throughway which you can join from Buffalo. From Montreal and Ottawa, simply find the I-15 in Rochester.
Your driving time will probably be 5-6 hours from Buffalo, NY - a little less from Rochester.
Coming from Pittsburg, PA - Cleveland, OH - Detroit, MI - Chicago, IL - or anywhere west of central Maryland:
The simplest is to follow The Pennsylvania Turnpike all the way from Pittsburg to Harrisburg and then follow the I-15 south from there. You can also make a shortcut: Shortly after the junction at Breezewood where I-70 splits off the Turnpike and goes south, you can get off the Turnpike onto Hwy 30 towards Chambersburg and Gettysburg. In Gettyburg, you find I-15 south toward Frederick, Maryland.
Your driving time will likely be 3-4 hours from Pittsburg.