Get a Venom-Ruby in Echo Bazaar

The fastest way I've found so far is in Mahogany Hall; it requires a very high Persuasive skill. If you train the Louche Devil and teach him Philosophy, you'll get 111 Nevercold Brass Slivers per action and increase your Pygmalion quality. When Pygmalion reaches 17 or 18, you should be safe to take him out to a Society dinner, which gives you 1000 bonus slivers. ... You can then re-train him as often as you like to rack up lots of Echoes.

If you want to do it with your Dangerous, head to the third coil of the Labyrinth of Tigers. "Avoid becoming an exhibit yourself" and "Fight back" for ~1 Echo per action. (Most of the actions in the third coil earn ~1 Echo per action, but they require a very high Persuasive as well.)

While most of these cards are dream cards that cause nightmares, even nightmares can be... educational if you manage to follow them all the way to the end of the dream. In general you will find them pretty annoying until you have some way of reliably removing nightmares, then you can make better use of them.