The Pan-American Highway passes through Tulcán, over the Rumichaca bridge and on into the Bolívar province of Colombia. The closest Colombian town to the border is Ipiales, about 2km (1 1/4 miles) north of the bridge.
The border process is relatively painless and cost free. Ecuadorean and Colombian immigration officials have their stations on either side of the bridge. If you're heading into Colombia, you will have the option of either a 30- or a 90-day visa. (Be sure to specify the latter if you think you'll need it.) The border offices are open daily from 6am until 8pm.
There are money-changers on both sides of the border, but you're best off changing for some Colombian pesos in Tulcán.
Given the precarious security situation in Colombia, you should always check with your home consulate, fellow travelers, and knowledgeable locals before heading across.
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