In city centre (no cars), next to everything. The apartment had everything we needed. It was clean, and the directions to check in after hours were clear, accurate and simple. We even tried to extend our stay, but unfortunately the apartment was already booked.
The complimentary Basel Card was a nice extra.
Highly recommended!
The only shortcoming was that we would have been happy to separate the garbage into categories for recycling, but there was a single bag for refuse.