Man, now that I'm reading up on it, I want to go there...
Lviv "teems with energy that can't be found anywhere else in the Ukraine" (Let's Go Eastern Europe, 2003) "Lviv's churches, squares, and ancient tenements create a city as splendid as Prague or St. Petersburg. With a heavy Polish and Austrian influence, the city has a Western air." (ibid.)
There isn't a huge long list of attractions - the market square with town hall, several churches, the remains of a synagogue, an old castle hill you climb for the view (it doesn't sound like the castle's there anymore), more cathedrals in a park, and a couple of museums...and a famous cafe culture. Everything looks pretty compact for looking around, the open air folk/architecture museum is the farthest out of town, and it's only 1.6 km, so very manageable transport wise. Sounds like an attractive and pretty laid back place to spend a couple of days - not a bad place to break that long haul journey between Krakow and Kyiv.
There's a couple of recommended hotels in my Let's Go (it's old, remember) Hotel Lviv and Hotel George. Check a more recent guidebook on the region for more details.
If you haven't already seen it, I just posted a very long story about my visit to Ukraine in the travel stories forum. Due to technical difficulties, it doesn't look as good as it did in Word, but if you ignore the symbol strings at the beginning and can plod through the text, you may be able to get something of interest out of it. I'm working on fixing it, but I don't know how yet. When I was leaving Ukraine I rode the train back through western Ukraine...mostly it struck me as lots and lots of farmland - beautiful, but maybe not ideal for a stopover. Sounds like Lviv would be your best bet.