Slack URL to open a channel from browser
Sure you can:
https://<organization>.slack.com/messages/<channel>/
for example: https://tikal.slack.com/messages/general/ (of course that for accessing it, you must be part of the team)
Referencing a channel within a conversation
To create a clickable reference to a channel in a Slack conversation, just type # followed by the channel name. For example: #general.
To grab a link to a channel through the Slack UI
To share the channel URL externally, you can grab its link by control-clicking (Mac) or right-clicking (Windows) on the channel name:
The link would look like this:
https://yourteam.slack.com/messages/C69S1L3SS
Note that this link doesn't change even if you change the name of the channel. So, it is better to use this link rather than the one based on channel's name.
To compose a URL for a channel based on channel name
https://yourteam.slack.com/channels/<channel_name>
Opening the above URL from a browser would launch the Slack client (if available) or open the slack channel on the browser itself.
To compose a URL for a direct message (DM) channel to a user
https://yourteam.slack.com/channels/<username>
The URI to open a specific channel in Slack app is:
slack://channel?id=<CHANNEL-ID>&team=<TEAM-ID>
You will probably need these resources of the Slack API to get IDs of your team and channel:
GET https://slack.com/api/team.infoGET https://slack.com/api/channels.list?exclude_archived=1
Here's the full documentation from Slack