Stick shift won't shift to 2d

2001 Jetta, 110,000 miles, manual transmission; will shift from 1 to 3, 4, and 5, and R, but not 2d; feels like some sort of obstruction in the stick shifter itself. Slight rattle underneath.

If you are lucky, it may only be a problem with the connection between the shift lever and the transmission. I believe your car has a pair of cables running from shift lever to the top of the trans. These can get stiff with age and corrosion, and there is a plastic part on one of them that is known to break. This stuff is located under the battery box, so is invisible normally.

The other possibility is much less enjoyable. It could be a problem of a bent or cracked shifting fork inside the transmission, or a chunk of a synchro ring that has broken off and is getting in the way. Not only does this require transmission removal to repair, but it carries the danger than a loose piece of metal inside the trans can get jammed between gear teeth - and cause the trans to lock up: In which case depressing in the clutch pedal wont help.